avformat/id3v2: Check avio_read() return code in id3v2_parse()

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7f5a04a9b50d_7087_mp3__mp3__tooSmallFinal.mp3
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>