macos UI: crash when quitting VLC with the window close

Scenario:

open UI and playback from terminal
close the window
ctrl + C

Might be reproducible in other scenario of course.

*** Terminating app due to uncaught exception 'NSRangeException', reason: 'Cannot remove an observer <VLCLibraryWindow 0x12e071800> for the key path "effectiveAppearance" from <VLCApplication 0x14de0d790> because it is not registered as an observer.'
*** First throw call stack:
(
        0   CoreFoundation                      0x0000000183dd32ec __exceptionPreprocess + 176
        1   libobjc.A.dylib                     0x00000001838ba788 objc_exception_throw + 60
        2   Foundation                          0x0000000184e8558c -[NSObject(NSKeyValueObserverRegistration) _removeObserver:forProperty:] + 628
        3   Foundation                          0x0000000184e852c4 -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:] + 136
        4   libmacosx_plugin.dylib              0x0000000103786020 -[VLCLibraryWindow dealloc] + 104
        5   Foundation                          0x0000000185586118 _NSKVOPerformWithDeallocatingObservable + 172
        6   Foundation                          0x0000000184ea3404 NSKVODeallocate + 180
        7   libobjc.A.dylib                     0x00000001838afc90 _ZN19AutoreleasePoolPage12releaseUntilEPP11objc_object + 212
        8   libobjc.A.dylib                     0x00000001838ac2fc objc_autoreleasePoolPop + 260
        9   libmacosx_plugin.dylib              0x00000001037b669c __CloseIntf_block_invoke + 136
        10  libmacosx_plugin.dylib              0x00000001037b65fc CloseIntf + 132
        11  libvlccore.9.dylib                  0x0000000100e59b64 module_unneed + 148
        12  libvlccore.9.dylib                  0x0000000100e5f534 intf_DestroyAll + 92
        13  libvlccore.9.dylib                  0x0000000100e45b98 libvlc_InternalCleanup + 108
        14  libvlc.12.dylib                     0x0000000100c9ad28 libvlc_release + 72
        15  vlc-osx-static                      0x000000010080b0e4 main + 1080
        16  dyld                                0x00000001838f60e0 start + 2360
)
libc++abi: terminating due to uncaught exception of type NSException

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