dsicinav: K&R formatting cosmetics
dsicinav: Bound-check the source buffer when needed

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
dsicinav: Clip the source size to the expected maximum

A packet larger than cin->bitmap_size does not make sense.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org