[MU4 Issue] External MIDI keyboard unable to play MuseScore instruments (Sound preview not working)

[rgreen5]

Describe the bug There has been a regression in MS4. Now, the MuseScore instruments cannot be played at all. Input is only possible in note input mode, which of course stops the user from using the software to test the various instrument sounds or to demo ideas without commiting them to notation.

To Reproduce

1. Ensure that your external MIDI keyboard is connected before launching MS4, and that the settings in Preferences > I/O are correct.
2. Create a jazz combo from the Template secion, for example.
3. Click on a rest in the top staff and play the MIDI keyboard. Try other staves as well.

Actual result: No sound.

Expected behavior

As MuseScore 2, the user should be able to click on any staff in non-note-input mode and be able to play the staff instrument.

Platform information OS: Linux Mint 20.1, Arch.: x86_64, MuseScore version (64-bit): 4.0.0-2059995262, revision: github-musescore-musescore-cafefd7 . Akai LPK25 USB keyboard.

[Tantacrul]

Assigned a P1 to this. Thanks!

[DmitryArefiev]

@vpereverzev @Eism Checked in latest master - still doesn't work

As a reference, it should work like in MuseScore 2 (it doesn't work in MuseScore 3 properly)

https://user-images.githubusercontent.com/90187801/184132594-d7122a26-43d4-4b45-a74c-774c9fcc40e3.mp4

[DmitryArefiev]

Fixed in #12879

But it doesn't work exactly as in MuseScore2, now it has fixed duration while playing MIDI keyboard. That's logged separately #13381