The 5-pin MIDI button in the top row of the app .... crashes

OS: macOS Mojave (10.14), Arch.: x86_64, MuseScore version (64-bit): 3.0.5.21343, revision: 58dd23d

At least if MIDI is connected. I tried to find out what it did -- I thought that perhaps I could block MIDI output if not using it. So I tried to see what the button did -- it crashes instantly.

Please fix these wholly-repeatabe MIDI crashes next round!