Fix feasibility pump with ScalarNonlinearFunction constraints

[odow]

Closes #263

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (05ae25e) 91.76% compared to head (ee6ddb5) 91.27%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #264 +/- ## ========================================== - Coverage 91.76% 91.27% -0.50% ========================================== Files 20 20 Lines 2065 1971 -94 ========================================== - Hits 1895 1799 -96 - Misses 170 172 +2 ```

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