Comment 2 for bug 1912129

When I close the Mixxx window, the window closes and sometimes a new, empty window pops up for a short amount of time. This is the terminal output:

```
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 33780, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 33798, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 33801, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 35140, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 35180, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 36478, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 37789, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 39157, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 39186, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 39189, resource id: 62914578, major code: 130 (Unknown), minor code: 3
Warning [Main]: QXcbConnection: XCB error: 8 (BadMatch), sequence: 40583, resource id: 62914578, major code: 130 (Unknown), minor code: 3
JackCallback: Stopping stream
RealProcess: Callback finished
Silencing the output
RealStop: Stream stopped
JackXRunCb: JACK signalled xrun
UpdateQueue: Removed stream from processing queue
TerminateHostApis in
TerminateHostApis out
Warning [LibraryScanner 1]: QSqlDatabasePrivate::removeDatabase: connection 'MIXXX-2' is still in use, all queries will cease to work.
Warning [Main]: The following 6 controls were leaked:
Warning [Main]: "[VinylControl]" "show_vinylcontrol" QObject(0x0)
Warning [Main]: "[Master]" "maximize_library" QObject(0x0)
Warning [Main]: "[Master]" "skin_settings" QObject(0x0)
Warning [Main]: "[Library]" "show_coverart" QObject(0x0)
Warning [Main]: "[Microphone]" "show_microphone" QObject(0x0)
Warning [Main]: "[PreviewDeck]" "show_previewdeck" QObject(0x0)
DEBUG ASSERT: "!"Controls were leaked!"" in function void MixxxMainWindow::finalize() at /home/jan/Projects/mixxx/src/mixxx.cpp:874
Aborted (core dumped)
```