ONBS not accepting .MID file extension (uppercase)

[piperwillow]

Describe the bug
ONBS won't open midi files with capital .MID file extension but will open the same file with lowercase .mid

To Reproduce
Steps to reproduce the behavior:

1. Drag and drop midi file with .MID file extension on the program or open directly from program.
2. If former, nothing happens; if latter "Error: This file cannot be opened in this program" pops up.

Expected behavior
To open the file without having to manually rename every time.

Screenshots

[Bentroen]

Had a go at fixing this recently, however, it looks like the string specifying the target file extensions for the open file dialog is somehow case-insensitive (even specifying deliberately .MID didn't work). I'll need to have a look at it again sometime.