Fix queryktharr() return value/behaviour. #4186
Merged
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Summary
Up to AMReX 24.07 (at least), ParmParse::queryktharr() used to return 0 if the given k (2nd parameter) was out of range.
As of AMReX 24.10, this is not the case, and ppindex() attempts to access found->second.m_vals out-of-bounds, resulting in seg-fault/undefined behaviour.
This PR reverts to the original behaviour, which is now consistent with the documentation for querykth() in AMReX_ParmParse.H. It also makes minor corrections to the associated comments to align with this behaviour.
Additional background
Checklist
The proposed changes: