avcodec/dpx_parser: reset index when finding a startcode, not after

This is simpler

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/dpx_parser: fix flushing end out

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/dpx_parser: Allow frame size to be too small

Fixes Ticket3402

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>