Problem: Int64 is not checked in gas related api

[mmsqe]

Closes: #XXX

Description

---

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

---

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

Attention: Patch coverage is 85.71429% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 63.32%. Comparing base (b216a32) to head (f437aea).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #425   +/-   ##
========================================
  Coverage    63.31%   63.32%           
========================================
  Files          130      130           
  Lines        12342    12342           
========================================
+ Hits          7814     7815    +1     
+ Misses        4014     4013    -1     
  Partials       514      514           

Files	Coverage Δ
rpc/backend/backend.go	78.94% <ø> (ø)
rpc/backend/node_info.go	46.97% <100.00%> (+0.46%)	⬆️
rpc/backend/call_tx.go	57.58% <0.00%> (ø)