fate: Convert the paletted output in the brenderpix tests to rgb24

This makes the output consistent on big-endian systems.
isom: Simplify mov_rewrite_dvd_sub_extradata()

This avoids the 2nd buffer and fixes the palette truncated check
isom: only write the size if its non zero in mov_rewrite_dvd_sub_extradata()

Sample-Id: NeroRecodeSample.mp4
mov: fill in subtitle dimensions after parsing tkhd

Sample-Id: NeroRecodeSample.mp4
mov: call mov_rewrite_dvd_sub_extradata() after parsing dimensions from tkhd

This also moves mov_rewrite_dvd_sub_extradata() to mov.c.

Sample-Id: NeroRecodeSample.mp4