Crash: Manage MIDI Devices window, testing appreciated

   Just fixed a crash when closing the Manage MIDI Devices dialog 
reported over at Debian:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1091859

   I've pushed the fix to master and it needs review and testing before 
I do a 24.12.1 release to get this fixed for everyone.

   To test, build the latest from master then open and close the Manage 
MIDI Devices window (Studio > Manage MIDI Devices).

   For more thorough testing, add and remove some devices.  Then maybe 
do some undo/redos.  And whatever else you usually do here.  Finally, 
close the window or even just create a new document while it is up.

   Hopefully you will encounter no crashes on close of the Manage MIDI 
Devices window.  Let me know if you do.

   If anyone wants to review the changes:

https://sourceforge.net/p/rosegarden/git/ci/64943ed3d8282fc9893129e69ed435057f55e759/

   It appears to have been an erase-while-iterating error.  I was unable 
to get it to crash, so I'm only guessing.

   I'll give this a week before going through the release process.  Any 
help anyone can provide is appreciated.  Thanks.  And let me know how it 
goes.

Ted.