libavcodec/xsubenc.c: Fix bounding box coordinates

Fix coordinates of the lower right corner of the text area.
Note that the coordinates are redundant as the size and
position of the text area are known.
Many decoders (including Sony Playstation 3, VLC and FFmpeg)
ignore the redundant coordinates.
Some hardware decoders need them for correct playback.

Verified on Philips DVD player models HTS7201 and DVP3380.

Fixes ticket #3031

Signed-off-by: Erik Olofsson <eaj.olofsson@gmail.com>
Reviewed-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
libavcodec/xsubenc.c: set coded_bits_per_sample

Explicitly set the number of bits per sample to stop
the avi muxer from guessing at 24 bits.
The result is that bits per pixel in the avi stream header
matches what other XSUB muxers produce, such as AVIAddXSubs.exe

Signed-off-by: Erik Olofsson <eaj.olofsson@gmail.com>
Reviewed-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>