avformat/mov: Check avio_read() return code in mov_read_extradata() and shrink the extradata if needed / return an error

Fixes use of uninitialized data
Fixes: msan_uninit-mem_7ff57193e77e_2715_RAW512K_Stream_004.mov
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>