avcodec/ffv1dec: check global header version

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
ffv1dec: check that global parameters dont change in version 0/1

Such changes are not allowed nor supported

Fixes Ticket2906

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