fix: method handler crash due to nil min fee per gas

[blindchaser]

Describe your changes and provide context

Fix method handler crashed caused by a nil value for the minimum base gas fee per gas.

Testing performed to validate your change

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 61.50%. Comparing base (5ddb9ab) to head (5742e69).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
x/evm/keeper/fee.go	40.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1982      +/-   ##
==========================================
- Coverage   61.57%   61.50%   -0.07%     
==========================================
  Files         263      263              
  Lines       24325    24328       +3     
==========================================
- Hits        14978    14964      -14     
- Misses       8237     8252      +15     
- Partials     1110     1112       +2     

Files with missing lines	Coverage Δ
x/evm/keeper/fee.go	84.12% <40.00%> (-4.21%)	⬇️

... and 2 files with indirect coverage changes