chore(tm): use the second return value of GetConsensusState to check if consensus state exists

[siburu]

Description

In some places, codes like below are used to check whether a consensus state exists or not.
I think this is not a bug, but a bit different from the intention of GetConsensusState.
Probably, callers of this function should see the second return value to check it.

if cons, _ := GetConsensusState(....); cons != nil {
    ....
}

Commit Message / Changelog Entry

chore(tm): use the second return value of GetConsensusState to check if consensus state exists

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[crodriguezvega]

Thank you, @siburu!

[codecov-commenter]

Codecov Report

Merging #3570 (8709a02) into main (8e9d797) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3570      +/-   ##
==========================================
- Coverage   78.76%   78.76%   -0.01%     
==========================================
  Files         182      182              
  Lines       12688    12687       -1     
==========================================
- Hits         9994     9993       -1     
  Misses       2262     2262              
  Partials      432      432              

Impacted Files	Coverage Δ
...light-clients/07-tendermint/misbehaviour_handle.go	85.43% <100.00%> (-0.15%)	⬇️
modules/light-clients/07-tendermint/update.go	87.50% <100.00%> (ø)

[damiannolan]

🙏