Fixes: runtime error: left shift of 706 by 22 places cannot be represented in type 'int'
See: L_shl() in the reference software
Fixes: 1609/clusterfuzz-testcase-minimized-5102163007111168

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