Properly catch hard crash

We crash hard when AMPL generates an error while evaluating the objective, e.g., when it emits
```
Error evaluating objective function: can't evaluate pow"(0,1.5).
```
Apparently, we don't properly catch such errors.

Start by reproducing the crash with the AMPL objective error shown in the issue, then trace the package's error-handling entry point for objective evaluation. Done means the AMPL error is caught and reported without a hard crash; no source file or test is named in the issue.

Written by the indexing model from the issue text.