vl/rbsp: fix another three byte not detected

vl/rbsp: fix another three byte not detected

This happens when three byte "00 00 03" is partly loaded to
vlc->buffer, thus at the bottom of buffer with valid bits is
"00" or "00 00" and left  like "00 03" or "03" in the data,
so that it will not be detected by three byte emulation check.
The reason for that is the escaped bit was set to 0 from the
rbsp init.

Signed-off-by: Leo Liu <leo.liu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>