mpv.desktop: add more ogg-related mime types

Also adds audio/ogg and video/ogg.
demux_disc: bluray: potentially fix some aspects of seeking

When flushing the AVIOContext, make sure it can't seek back to discarded
data. buf_ptr is just the current read position, while buf_end - buffer
is the actual buffer size. Since mpegts.c is littered with seek calls,
it might be that the ability to seek could read

Mark the stream (which the demuxer uses) as not seekable. The cache can
enable seeking again (this behavior is sometimes useful for other
things). I think this should have had no bad influence in theory, since
seeking BD/DVD first does the "real" seek, then flushes libavformat and
reads new packets.
demux_lavf: bluray: don't skip stream data when flushing

This code meant to flush demuxer internal buffers by doing a byte seek
to the current position. In theory this shouldn't drop any stream data.
However, if the stream positions mismatch, then avio_seek() (called by
av_seek_frame()) stops being a no-op, and might for example read some
data to skip to the seek target. (This can happen if the distance is
less than SHORT_SEEK_THRESHOLD.)

The positions get out of sync because we drop data at one point (which
is what we _want_ to do). Strictly speaking, the AVIOContext flushing is
done incorrectly, becuase pb->pos points to the start of the buffer, not
the current position. So we have to increment pb->pos by the buffered
amount.

Since there are other weird reasons why the positions might go out of
sync (such as stream_dvd.c dropping buffers itself), and they don't
necessarily need to be in sync in the first place unless AVIOContext has
nothing buffered internally, just use the sledgehammer approach and
correct the position manually.

Also run av_seek_frame() after this. Currently, it shouldn't read
anything, but who knows how that might change with future libavformat
development.

This whole change didn't have any observable effect for me, but I'm
hoping it fixes a reported problem.
cache_file: refuse to cache unseekable streams

This makes no sense to use with DVD/BD/DVB and some others, and these
streams happen to be unseekable.

Also, other kinds of unseekable streams (like reading from pipe) should
work, but will exhibit sketchy behavior if they need to seek. So just
disable it, and leave these problems to the memory cache (cache.c).
stream: don't drop buffers on failed seeks

Might matter when libavformat tries to do tiny seekbacks in an
unseekable stream, and the seekback buffer isn't large enough. In this
case, seeking would fail, and would drop the current buffer. The
seekback would end up dropping future data.

This change probably doesn't have any observable effects. libavformat
normally has its own stream buffer, and demux_mkv.c tries carefully
never to seek back.
demux_disc: export BD/DVD audio language

This was "forgotten".
x11: always wait for mapped when using --wid

Might help with embedding with mozplugger. I can't confirm whether it
fixes the issue.

See #1090.