avformat/mov: check atom nesting depth

Fixes call stack overflow
Fixes: case1_call_stack_overflow.mp4
Found-by: Michal Zalewski <lcamtuf@coredump.cx>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/mov: fix integer overflow of size

Fixes: case1_call_stack_overflow.mp4
Found-by: Michal Zalewski <lcamtuf@coredump.cx>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swscale: increase yuv2rgb table headroom

Fixes out of array access
Fixes: case2_bad_read_yuv2rgbx32.mp4
Found-by: Michal Zalewski <lcamtuf@coredump.cx>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>