Check result index in get_fallback of ConstraintPrimal

[blegat]

Follow up of #1682

[odow]

I considered this, but I wasn't convinced it was the right approach.

Solvers using the get_fallback can call check_result_index_bounds in their method. It doesn't have to be in the get_fallback.

This is also inconsistent with the other get_fallback method which don't check that the result is in-bounds.

It also means for the caching optimizer method that we enter the try, potentially throw a result-index error, enter the catch, and then re-throw the error.

I decided it was simpler just to check before the try-catch.

[blegat]

Solvers using the get_fallback can call check_result_index_bounds in their method. It doesn't have to be in the get_fallback.

Yes but we might as well do it once in get_fallback rather than everywhere it's called from.

This is also inconsistent with the other get_fallback method which don't check that the result is in-bounds.

The other ones should be changed. They were written in a time we were not checking these result bounds yet.

It also means for the caching optimizer method that we enter the try, potentially throw a result-index error, enter the catch, and then re-throw the error.

That's worrying. It could also catch an InvalidIndex error. Shouldn't the catch check that the error is what it expects and rethrow otherwise ?