MPVActivity: Fix invisible pause button for audio files
MPVActivity: Fix invisible pause button for audio files

The `pause` event observer does not seem to get invoked
if only a cover or no video is present.

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