Allow replace the patch in Patman with a drag/drop

https://github.com/LMMS/lmms/blob/2eea79bdd349a0b385c9a371e0dc6c8dccfc5b6d/plugins/Patman/Patman.cpp#L601

And,
https://github.com/LMMS/lmms/blob/2eea79bdd349a0b385c9a371e0dc6c8dccfc5b6d/plugins/Patman/Patman.cpp#L579

Two places use "samplefile" word, while the dropped in file comes with: "patchfile" request.
This is prohibiting replacement of the sample when .pat file is dropped in.

Linking: #7849 too.

Open plugins/Patman/Patman.cpp at the references around lines 579 and 601, then compare how the drag/drop request names the incoming file with the two uses of "samplefile". The change is complete when dropping a .pat file allows the existing sample to be replaced; review linked issue #7849 for related context.

Written by the indexing model from the issue text.