MPVView: disable video output before destroying GL
MPVView: disable video output before destroying GL

Otherwise mpv fails to output video, sends EOF and we get back to the file picker.

mpv-android/mpv-android,mpv-android/mpv-android,mpv-android/mpv-android,jeeb/mpv-android,mpv-android/mpv-android,jeeb/mpv-android,jeeb/mpv-android,mpv-android/mpv-android,jeeb/mpv-android,jeeb/mpv-android