avcodec/sgirledec: fix () in RBG323_TO_BGR8() macro

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat: add format_probesize to allow tuning the maximum amount of bytes to identify the filetype

Currently probesize is cliped at 1mb before being used for format detection.
Alternatively this cliping could be removed but this would then tie various
things like stream analysis to the file detection.

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