Emit ended only on eof end-file reason

[kKaskak]

ShellVideo emitted ended for every mpv end-file event, including the stop caused by loading the next video, which made the player skip episodes when binge watching. Only emit ended for eof. Older shells report "other" for all non-error reasons so they keep the current behavior.

[kKaskak]

regression found: EOF was emitted sometimes because of network disconnect etc
workaround in #151

correct implementation needs correct retry on http errors coming from addons
via ffmpeg http protocol docs

• mpv says EOF can happen on interrupted remote network playback, not only natural media end:
  https://raw.githubusercontent.com/mpv-player/mpv/master/include/mpv/client.h

• mpv stream-lavf-o is the correct place to pass FFmpeg/libavformat stream AVOptions: https://mpv.io/manual/stable/#options-stream-lavf-o

• FFmpeg reconnect means reconnect before EOF, while reconnect_at_eof treats EOF as an error and is described as useful for live/endless
  streams, so I would not use reconnect_at_eof for VOD: https://ffmpeg.org/ffmpeg-protocols.html#http

• mpv loadfile replace stops current playback and plays a new item, which is exactly the path we should avoid here:
  https://mpv.io/manual/stable/#command-interface-loadfile