Fixes: out of array access
Fixes: 21469/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_G2M_fuzzer-5199357982015488

Alternatively the arrays can be made bigger or the index can be clipped.
In case a real file with such huge tiles exist we ask the user to upload it.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>