fix(x/ecocredit): fix create batch issuance with same recipient

[ryanchristo]

Description

Closes: #1139

Fixes create batch to account for issuance with same recipient.

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[codecov]

Codecov Report

Merging #1144 (723afc8) into master (530130f) will increase coverage by 0.01%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master    #1144      +/-   ##
==========================================
+ Coverage   69.27%   69.28%   +0.01%     
==========================================
  Files         220      220              
  Lines       22786    22801      +15     
==========================================
+ Hits        15784    15797      +13     
- Misses       5624     5626       +2     
  Partials     1378     1378              

Flag	Coverage Δ
experimental-codecov	69.35% <77.77%> (+0.01%)	⬆️
stable-codecov	63.63% <77.77%> (-0.01%)	⬇️

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[technicallyty]

lgtm! just one spot we can use a util function 👍🏻

[clevinson]

Nice catch -- should we also check again that BatchMint doesn't override balances?

-- edit: Just checked, seems like we handle things correctly in BatchMint :)