avcodec/rangecoder: Test for invalid corner case

Fixes runtime error: left shift of 1912602815 by 8 places cannot be represented in type 'int'
Fixes: 1403/clusterfuzz-testcase-minimized-4724820484816896

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
