avcodec/hevc_cabac: Check for ff_init_cabac_decoder() failure in cabac_reinit()

Fixes: runtime error: left shift of negative value -967831544
Fixes: 2815/clusterfuzz-testcase-minimized-6062914471460864

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