min-gas-multiplier parameter should accept zero value

[yihuang]

Description

update min-gas-multiplier validation logic

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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 #1120 (4a515ae) into main (b567624) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1120   +/-   ##
=======================================
  Coverage   61.86%   61.86%           
=======================================
  Files          88       88           
  Lines        7285     7285           
=======================================
  Hits         4507     4507           
  Misses       2557     2557           
  Partials      221      221           

Impacted Files	Coverage Δ
types/account.go	26.31% <100.00%> (ø)
x/feemarket/types/params.go	93.10% <100.00%> (ø)

[crypto-facs]

Great catch! Forgot to update this from the divider version 🙏

[fedekunze]

ACK, can you add a changelog entry?

[yihuang]

ACK, can you add a changelog entry?

done