h264: fix use of uninitialized variable

Fixed CID968588

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
h264: print mismatching opcode details in check_opcodes()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
h264/ff_generate_sliding_window_mmcos: fix use of uninitialized variable

Fixes CID968587
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>