subreader: fix one more unsafe sscanf call with "%["

"%[,.:]" conversion was used with a buffer that could be shorter than
the matched string. Suppress assignment of the conversion since the
value wasn't used anyway, and also limit match length to 1 as it
doesn't look like the intent was to match longer runs of the
characters.

Merged from mplayer2 commit 5cb9aac. Note that the other half of the
mplayer2 commit is already part of the mpv commit d98e61e. (I'm not
sure why. The mplayer2 commit date precedes mpv's, but was pushed long
after the mpv change was pushed; either one of the dates is wrong, or
we did the same work twice - in that case, thanks a lot...)
img_format: fix broken condition

This caused all formats with fewer than 8 bits per component marked as
little endian. (Normally, only some messed up packed RGB formats are
endian-specific in this case.)
vf_yadif: actually set PTS for output frames

The original frame PTS was used instead. Oops...
Fix some cppcheck / scan-build warnings

These were found by the cppcheck and scan-build static analyzers. Most
of these aren't interesting (the 2 previous commits fix some interesting
cases found by these analyzers), and they don't nearly fix all warnings.
(Most of the unfixed warnings are spam, things MPlayer never cared
about, or false positives.)
demux: remove retrieval of chapter end time

The frontend doesn't use this.

Also use double for returning the chapter times. Everything uses double
for times, and there's no reason to use float here.
stream: report chapter times, use time seeks for DVD chapters

Allow the stream layer to report chapter times. Extend stream_dvd to do
this. I'm not 100% sure whether the re-used code is bug-free (because it
was used for slave-mode and/or debugging only).

MAke the frontend do time-based seeks when switching DVD chapters. I'm
not sure if there's a real reason STREAM_CTRL_SEEK_TO_CHAPTER exists
(maybe/hopefully not), but we will see.

Note that querying chapter times in demuxer_chapter_time() with the new
STREAM_CTRL_GET_CHAPTER_TIME could be excessively slow, especially with
the cache enabled. The frontend likes to query chapter times very often.
Additionally, stream_dvd uses some sort of quadratic algorithm to list
times for all chapters. For this reason, we try to query all chapters on
start (after the demuxer is opened), and add the chapters to the demuxer
chapter list. demuxer_chapter_time() will get the time from that list,
instead of asking the stream layer over and over again.

This assumes stream_dvd knows the list of chapters at the start, and
also  that the list of chapters never changes during playback. This
seems to be true, and the only exception, switching DVD titles, is not
supported at runtime (and doesn't need to be supported).
demux: don't name unknown chapters "unknown"

The frontend's fallback for missing chapter names is better.