Add missing error checks for etag errors

[yaron2]

This PR adds a few nil error checks for state stores. A follow up for #579

[codecov]

Codecov Report

Merging #584 (3a76cf7) into master (4d3e1be) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #584      +/-   ##
==========================================
- Coverage   30.61%   30.61%   -0.01%     
==========================================
  Files          85       85              
  Lines        7107     7111       +4     
==========================================
+ Hits         2176     2177       +1     
- Misses       4697     4699       +2     
- Partials      234      235       +1     

Impacted Files	Coverage Δ
state/aerospike/aerospike.go	19.29% <0.00%> (-0.35%)	⬇️
state/azure/tablestorage/tablestorage.go	14.43% <0.00%> (-0.31%)	⬇️
state/cloudstate/cloudstate_crdt.go	9.01% <0.00%> (+0.42%)	⬆️

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