qml_video example did not stop after the window closed

[on-chip-man]

when I close the aml_vedio example ,the application does not stop, it seems that the QMutexLocker is locked and waiting forever

[valbok]

Hi, thanks for contributing. Could you please share is it Android or Windows? What Qt version is used? Thanks

[on-chip-man]

thanks! Qt 5.15.2, Windows 10, msvc64

[on-chip-man]

I have figured out that in QAVDemuxer::unload(), we need unlock before avformat_close_input(&d->ctx);, otherwise it will lock forever in decode_interrupt_cb

[valbok]

#412