[Bindings] Add a missing null check

[vivien-apple]

Problem

This PR checks if the newly allocated connectionCallback object is not null.

[github-actions]

PR #25534: Size comparison from 4203370 to bc5a971

Increases (1 build for linux)

platform	target	config	section	4203370	bc5a9711	change	% change
linux	thermostat-no-ble	arm64	(read only)	2520900	2520964	64	0.0
			.text	2107712	2107776	64	0.0

Decreases (1 build for cc32xx)

platform	target	config	section	4203370	bc5a9711	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	2026706	20267066	-1	-0.0

Full report (5 builds for cc32xx, linux, qpg)

platform	target	config	section	4203370	bc5a9711	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	644425	644425	0	0.0
			(read/write)	203688	203688	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197088	197088	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	930235	930235	0	0.0
			.debug_aranges	87336	87336	0	0.0
			.debug_frame	300028	300028	0	0.0
			.debug_info	2026706	20267066	-1	-0.0
			.debug_line	2659698	2659698	0	0.0
			.debug_loc	2802749	2802749	0	0.0
			.debug_ranges	282952	282952	0	0.0
			.debug_str	3023892	3023892	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105929	105929	0	0.0
			.shstrtab	232	232	0	0.0
			.stab	204	204	0	0.0
			.stabstr	441	441	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	378514	378514	0	0.0
			.symtab	256624	256624	0	0.0
			.text	536372	536372	0	0.0
linux	chip-tool-ipv6only	arm64	(read only)	12156404	12156404	0	0.0
			(read/write)	733448	733448	0	0.0
			.bss	34296	34296	0	0.0
			.data	3008	3008	0	0.0
			.data.rel.ro	675552	675552	0	0.0
			.dynamic	560	560	0	0.0
			.got	15376	15376	0	0.0
			.init	24	24	0	0.0
			.init_array	216	216	0	0.0
			.rodata	588308	588308	0	0.0
			.text	9827476	9827476	0	0.0
	thermostat-no-ble	arm64	(read only)	2520900	2520964	64	0.0
			(read/write)	145224	145224	0	0.0
			.bss	56344	56344	0	0.0
			.data	1784	1784	0	0.0
			.data.rel.ro	77688	77688	0	0.0
			.dynamic	560	560	0	0.0
			.got	5360	5360	0	0.0
			.init	24	24	0	0.0
			.init_array	432	432	0	0.0
			.rodata	150800	150800	0	0.0
			.text	2107712	2107776	64	0.0
qpg	lighting-app	qpg6105+debug	(read/write)	1152020	1152020	0	0.0
			.bss	99812	99812	0	0.0
			.data	852	852	0	0.0
			.text	599116	599116	0	0.0
	lock-app	qpg6105+debug	(read/write)	1119084	1119084	0	0.0
			.bss	96292	96292	0	0.0
			.data	864	864	0	0.0
			.text	566184	566184	0	0.0