fix: use GetParamsIfExists() to fetch old params

[blindchaser]

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Testing performed to validate your change

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.67%. Comparing base (c2a0d85) to head (f3df470).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1842      +/-   ##
==========================================
- Coverage   60.69%   60.67%   -0.03%     
==========================================
  Files         259      259              
  Lines       22748    22752       +4     
==========================================
- Hits        13808    13804       -4     
- Misses       7956     7966      +10     
+ Partials      984      982       -2     

Files with missing lines	Coverage Δ
x/evm/keeper/params.go	74.28% <100.00%> (+3.31%)	⬆️
x/evm/migrations/migrate_deliver_tx_gas_limit.go	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes