getbits: do not call get_bits(0) for coded value 0 in dav1d_get_vlc
getbits: do not call get_bits(0) for coded value 0 in dav1d_get_vlc

Fixes clusterfuzz-testcase-minimized-dav1d_fuzzer-5669943870226432. Credits to
oss-fuzz.

videolan/dav1d