codecparsers: h264: fix rbsp_more_data() implementation.

codecparsers: h264: fix rbsp_more_data() implementation.

Account for trailing zero bits when checking for rbsp_more_data().

In particular, fix an hypothetical stream whereby rbsp_more_data()
is called in the following conditions for PPS header: NalReader
reached position 20, 12 bits are remaining and trailing data at
current byte position is c8 00.

rbsp_more_data() used to return TRUE whereas it should obviously
return FALSE because x8 00 represents a valid rbsp_trailing_bits()
structure.

https://bugzilla.gnome.org/show_bug.cgi?id=685890

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>