Fix != 0 check in rvsol

[mininny]

Description

Using bitwise not on a 0 padded uint256 value results in the value being uint256.max when it should be 1.

Use eq(x,0) to check for not instead.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.89%. Comparing base (8ff9318) to head (e5a5842).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #113   +/-   ##
=======================================
  Coverage   61.89%   61.89%           
=======================================
  Files          27       27           
  Lines        4091     4091           
=======================================
  Hits         2532     2532           
  Misses       1427     1427           
  Partials      132      132           

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