MPVView: Limit demuxer cache size correctly
MPVView: Limit demuxer cache size correctly

The backbuffer has a separate limit, which defaults to 400MB too.
jeeb/mpv-android,jeeb/mpv-android,jeeb/mpv-android,mpv-android/mpv-android,mpv-android/mpv-android,jeeb/mpv-android,mpv-android/mpv-android,mpv-android/mpv-android,jeeb/mpv-android,mpv-android/mpv-android