properly treat commitSnapshot error

[BeniaminDrasovean]

Description of the reasoning behind the pull request (what feature was missing / how the problem was manifesting itself / what was the motive behind the refactoring)

• If the node is closing during a trie snapshot, some nodes will not be retrieved from storage because the dbs are closed, thus automatically triggering the syncing process for those nodes.

Proposed Changes

• If the reason for which the nodes can not be retrieved from storage is because the node is closing, do not try to sync those nodes.

Testing procedure

• Normal testing procedure

[codecov-commenter]

Codecov Report

Base: 70.73% // Head: 70.74% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (c252312) compared to base (f7c9429).
Patch coverage: 50.00% of modified lines in pull request are covered.

Additional details and impacted files

@@              Coverage Diff              @@
##           rc/v1.4.0    #4513      +/-   ##
=============================================
+ Coverage      70.73%   70.74%   +0.01%     
=============================================
  Files            624      624              
  Lines          83297    83304       +7     
=============================================
+ Hits           58916    58936      +20     
+ Misses         19973    19966       -7     
+ Partials        4408     4402       -6     

Impacted Files	Coverage Δ
state/accountsDB.go	76.82% <0.00%> (-0.31%)	⬇️
trie/node.go	84.25% <66.66%> (+0.78%)	⬆️
trie/branchNode.go	79.52% <100.00%> (+1.25%)	⬆️
trie/extensionNode.go	72.26% <100.00%> (+1.79%)	⬆️
common/pidQueue.go	93.33% <0.00%> (-3.34%)	⬇️
debug/resolver/interceptorResolver.go	77.77% <0.00%> (-1.34%)	⬇️
consensus/broadcast/delayedBroadcast.go	86.21% <0.00%> (+1.40%)	⬆️

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[gabi-vuls]

System test passed.