fix: close iterators

[albertchon]

Iterators should be closed after use.

I'd also potentially recommend renaming GetContractState(ctx sdk.Context, contractAddress sdk.AccAddress) sdk.Iterator to GetContractStateIterator(ctx sdk.Context, contractAddress sdk.AccAddress) sdk.Iterator so it's clear that clients should close the iterator themselves or simply change the function signature to take a callback so the usage pattern is standardized.

[codecov]

Codecov Report

Merging #792 (1c9a1e1) into master (16ea5b0) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #792      +/-   ##
==========================================
+ Coverage   58.64%   58.76%   +0.11%     
==========================================
  Files          50       50              
  Lines        5845     5857      +12     
==========================================
+ Hits         3428     3442      +14     
+ Misses       2166     2165       -1     
+ Partials      251      250       -1     

Impacted Files	Coverage Δ
x/wasm/keeper/genesis.go	89.74% <100.00%> (+0.13%)	⬆️
x/wasm/keeper/keeper.go	88.09% <100.00%> (+0.54%)	⬆️
x/wasm/keeper/legacy_querier.go	70.52% <100.00%> (+0.63%)	⬆️

[alpe]

Thanks a lot for your contribution! 💪 . Good 👀 !
I agree with your proposal to modify GetContractState and standardize using callbacks. I will do a PR

[alpe]

Nice 💯