Problem: no int64 check in error msg

[mmsqe]

Closes: #XXX

Description

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #388 (ac2cb26) into release/v0.20.x-cronos (0cd23d4) will not change coverage.
Report is 1 commits behind head on release/v0.20.x-cronos.
The diff coverage is 100.00%.

Additional details and impacted files

@@                   Coverage Diff                   @@
##           release/v0.20.x-cronos     #388   +/-   ##
=======================================================
  Coverage                   56.80%   56.80%           
=======================================================
  Files                         113      113           
  Lines                       10595    10595           
=======================================================
  Hits                         6018     6018           
  Misses                       4324     4324           
  Partials                      253      253           

Files	Coverage Δ
app/ante/fees.go	96.84% <100.00%> (ø)