GetCurrentDealInfo err: handle correctly err case

[nonsense]

Fixes: #7345

---

When GetCurrentDealInfo returns an error, such as:

		return nil, xerrors.Errorf(
			"deal %d not found "+
				"- deal may not have completed sealing before deal proposal "+
				"start epoch, or deal may have been slashed",
			dealID)

we should just note that we can't recover that deal, mark it as failed, and later remove the sector.

At the moment when GetCurrentDealInfo returns an error, we continue below the if-condition check for err and we throw a nil pointer exception and crash.

[codecov]

Codecov Report

Merging #7346 (6059535) into master (6df17bc) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #7346      +/-   ##
==========================================
+ Coverage   39.09%   39.14%   +0.04%     
==========================================
  Files         614      614              
  Lines       64995    64996       +1     
==========================================
+ Hits        25410    25440      +30     
+ Misses      35172    35147      -25     
+ Partials     4413     4409       -4     

Impacted Files	Coverage Δ
extern/storage-sealing/states_failed.go	12.60% <100.00%> (+1.25%)	⬆️
storage/wdpost_sched.go	77.22% <0.00%> (-1.99%)	⬇️
extern/sector-storage/sched_worker.go	78.38% <0.00%> (ø)
chain/messagepool/messagepool.go	57.17% <0.00%> (+0.24%)	⬆️
miner/miner.go	55.62% <0.00%> (+0.33%)	⬆️
chain/sync.go	65.27% <0.00%> (+0.33%)	⬆️
storage/wdpost_changehandler.go	98.58% <0.00%> (+0.47%)	⬆️
chain/actors/builtin/miner/v5.go	54.46% <0.00%> (+0.61%)	⬆️
chain/sync_manager.go	67.39% <0.00%> (+0.62%)	⬆️
chain/store/store.go	64.37% <0.00%> (+0.70%)	⬆️
... and 5 more

---

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[jennijuju]

backported in v1.11.3-rc2