Don't touch member variables from async dispatch.

[woody-apple]

We were null-checking members, then calling them from an async block,
by which point they might be null.

Fixes #21453

Problem

Crashes.

Change overview

See above.

Testing

Need to do stress-testing to see how this does on the crash stacks we are seeing...

[github-actions]

PR #21506: Size comparison from c5e7ab6 to c39c4c2

Increases (3 builds for bl602, k32w, telink)

platform	target	config	section	c5e7ab6	c39c4c2	change	% change
bl602	lighting-app	bl602+rpc	.text	1084056	1084060	4	0.0
k32w	lock	k32w0+release	(read/write)	701496	701512	16	0.0
			.text	626532	626548	16	0.0
telink	light-switch-app	tlsr9518adk80d	text	567938	567940	2	0.0

Decreases (2 builds for nrfconnect, telink)

platform	target	config	section	c5e7ab6	c39c4c2	change	% change
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	(read/write)	1180935	1180919	-16	-0.0
			text	815508	815504	-4	-0.0
telink	lighting-app	tlsr9518adk80d	(read/write)	820928	820920	-8	-0.0
			text	584802	584800	-2	-0.0

Full report (32 builds for bl602, cc13x2_26x2, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, p6, telink)

platform	target	config	section	c5e7ab6	c39c4c2	change	% change
bl602	lighting-app	bl602	(read/write)	1382250	1382250	0	0.0
			.bss	117626	117626	0	0.0
			.data	4480	4480	0	0.0
			.text	1052364	1052364	0	0.0
		bl602+rpc	(read/write)	1427682	1427682	0	0.0
			.bss	125066	125066	0	0.0
			.data	4600	4600	0	0.0
			.text	1084056	1084060	4	0.0
cc13x2_26x2	all-clusters-app	LP_CC2652R7	(read only)	669707	669707	0	0.0
			(read/write)	181676	181676	0	0.0
			.bss	74276	74276	0	0.0
			.data	3372	3372	0	0.0
			.rodata	88467	88467	0	0.0
			.text	580924	580924	0	0.0
	all-clusters-minimal-app	LP_CC2652R7	(read only)	635227	635227	0	0.0
			(read/write)	157844	157844	0	0.0
			.bss	73556	73556	0	0.0
			.data	3372	3372	0	0.0
			.rodata	77691	77691	0	0.0
			.text	557212	557212	0	0.0
	lock-ftd	LP_CC2652R7	(read only)	672567	672567	0	0.0
			(read/write)	169000	169000	0	0.0
			.bss	71348	71348	0	0.0
			.data	3296	3296	0	0.0
			.rodata	76535	76535	0	0.0
			.text	595552	595552	0	0.0
	lock-mtd	LP_CC2652R7	(read only)	655139	655139	0	0.0
			(read/write)	182116	182116	0	0.0
			.bss	67036	67036	0	0.0
			.data	3296	3296	0	0.0
			.rodata	101531	101531	0	0.0
			.text	553128	553128	0	0.0
	pump-app	LP_CC2652R7	(read only)	681055	681055	0	0.0
			(read/write)	161320	161320	0	0.0
			.bss	71388	71388	0	0.0
			.data	3296	3296	0	0.0
			.rodata	88919	88919	0	0.0
			.text	591652	591652	0	0.0
	pump-controller-app	LP_CC2652R7	(read only)	666631	666631	0	0.0
			(read/write)	175880	175880	0	0.0
			.bss	71524	71524	0	0.0
			.data	3292	3292	0	0.0
			.rodata	84743	84743	0	0.0
			.text	581408	581408	0	0.0
	shell	LP_CC2652R7	(read only)	662406	662406	0	0.0
			(read/write)	184496	184496	0	0.0
			.bss	76596	76596	0	0.0
			.data	3376	3376	0	0.0
			.rodata	85446	85446	0	0.0
			.text	576644	576644	0	0.0
cyw30739	light	cyw930739m2evb_01	(read/write)	583742	583742	0	0.0
			.app_xip_area	460696	460696	0	0.0
			.bss	65632	65632	0	0.0
			.data	744	744	0	0.0
			.rodata	0	0	0	0.0
			.text	112	112	0	0.0
	lock	cyw930739m2evb_01	(read/write)	589998	589998	0	0.0
			.app_xip_area	462200	462200	0	0.0
			.bss	70384	70384	0	0.0
			.data	748	748	0	0.0
			.rodata	0	0	0	0.0
			.text	112	112	0	0.0
	ota-requestor-no-progress-logging	cyw930739m2evb_01	(read/write)	589458	589458	0	0.0
			.app_xip_area	467220	467220	0	0.0
			.bss	64880	64880	0	0.0
			.data	688	688	0	0.0
			.rodata	0	0	0	0.0
			.text	112	112	0	0.0
efr32	lighting-app	BRD4161A	(read/write)	1088960	1088960	0	0.0
			.bss	133268	133268	0	0.0
			.data	2064	2064	0	0.0
			.text	953608	953608	0	0.0
		BRD4161A+rpc	(read/write)	1143300	1143300	0	0.0
			.bss	149948	149948	0	0.0
			.data	2276	2276	0	0.0
			.text	991056	991056	0	0.0
		BRD4161A+rs911x	(read/write)	974256	974256	0	0.0
			.bss	161744	161744	0	0.0
			.data	2048	2048	0	0.0
			.text	810444	810444	0	0.0
	lock-app	BRD4161A+wf200	(read/write)	1130096	1130096	0	0.0
			.bss	144400	144400	0	0.0
			.data	2056	2056	0	0.0
			.text	983620	983620	0	0.0
	window-app	BRD4161A	(read/write)	1082252	1082252	0	0.0
			.bss	134748	134748	0	0.0
			.data	2092	2092	0	0.0
			.text	945388	945388	0	0.0
esp32	all-clusters-app	c3devkit	(read only)	1024394	1024394	0	0.0
			(read/write)	1487042	1487042	0	0.0
			.dram0.bss	70336	70336	0	0.0
			.dram0.data	14600	14600	0	0.0
			.flash.rodata	216672	216672	0	0.0
			.flash.text	1024394	1024394	0	0.0
			.iram0.text	62902	62902	0	0.0
		m5stack	(read only)	1077863	1077863	0	0.0
			(read/write)	489064	489064	0	0.0
			.dram0.bss	75840	75840	0	0.0
			.dram0.data	34144	34144	0	0.0
			.flash.rodata	247084	247084	0	0.0
			.flash.text	1072479	1072479	0	0.0
			.iram0.text	123267	123267	0	0.0
k32w	light	k32w0+release	(read/write)	643368	643368	0	0.0
			.bss	69720	69720	0	0.0
			.data	2044	2044	0	0.0
			.text	568876	568876	0	0.0
	lock	k32w0+release	(read/write)	701496	701512	16	0.0
			.bss	70184	70184	0	0.0
			.data	2052	2052	0	0.0
			.text	626532	626548	16	0.0
linux	chip-tool-ipv6only	arm64	(read only)	9889452	9889452	0	0.0
			(read/write)	676865	676865	0	0.0
			.bss	32897	32897	0	0.0
			.data	3272	3272	0	0.0
			.data.rel.ro	622200	622200	0	0.0
			.dynamic	560	560	0	0.0
			.got	13536	13536	0	0.0
			.init	24	24	0	0.0
			.init_array	192	192	0	0.0
			.rodata	470140	470140	0	0.0
			.text	7841300	7841300	0	0.0
	thermostat-no-ble	arm64	(read only)	2349308	2349308	0	0.0
			(read/write)	141761	141761	0	0.0
			.bss	55329	55329	0	0.0
			.data	1672	1672	0	0.0
			.data.rel.ro	75976	75976	0	0.0
			.dynamic	560	560	0	0.0
			.got	5016	5016	0	0.0
			.init	24	24	0	0.0
			.init_array	408	408	0	0.0
			.rodata	139316	139316	0	0.0
			.text	1972480	1972480	0	0.0
mbed	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2453224	2453224	0	0.0
			.bss	214548	214548	0	0.0
			.data	5872	5872	0	0.0
			.text	1415868	1415868	0	0.0
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	(read/write)	1180935	1180919	-16	-0.0
			bss	143224	143224	0	0.0
			rodata	143344	143344	0	0.0
			text	815508	815504	-4	-0.0
	all-clusters-minimal-app	nrf52840dk_nrf52840	(read/write)	1160811	1160811	0	0.0
			bss	142460	142460	0	0.0
			rodata	134876	134876	0	0.0
			text	804656	804656	0	0.0
p6	all-clusters-app	default	(read only)	881528	881528	0	0.0
			(read/write)	1689268	1689268	0	0.0
			.bss	149168	149168	0	0.0
			.data	2648	2648	0	0.0
			.text	1529064	1529064	0	0.0
	all-clusters-minimal-app	default	(read only)	882248	882248	0	0.0
			(read/write)	1633300	1633300	0	0.0
			.bss	148448	148448	0	0.0
			.data	2648	2648	0	0.0
			.text	1473816	1473816	0	0.0
	light-app	default	(read only)	890568	890568	0	0.0
			(read/write)	1553348	1553348	0	0.0
			.bss	140336	140336	0	0.0
			.data	2440	2440	0	0.0
			.text	1402184	1402184	0	0.0
	lock-app	default	(read only)	886072	886072	0	0.0
			(read/write)	1591988	1591988	0	0.0
			.bss	144816	144816	0	0.0
			.data	2456	2456	0	0.0
			.text	1436328	1436328	0	0.0
telink	light-switch-app	tlsr9518adk80d	(read/write)	800512	800512	0	0.0
			bss	70808	70808	0	0.0
			noinit	40416	40416	0	0.0
			text	567938	567940	2	0.0
	lighting-app	tlsr9518adk80d	(read/write)	820928	820920	-8	-0.0
			bss	71652	71652	0	0.0
			noinit	40416	40416	0	0.0
			text	584802	584800	-2	-0.0