Add missing initialization for AVProbeData.

This has become necessary since the new mime field was added.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
proresenc_kostya: remove unneeded parameters

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
proresenc_kostya: report buffer overflow

If the allocated size, despite best efforts, is too small, exit
with the appropriate error.

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