H.265 NAL always have 2 bytes of headers. Unlike the H.264 parser, this parser
will simply return that there is NO_NAL if some of these bytes are missing.
This is then properly special cased by parsers and decoders. Add a test to
ensure we don't break this in the future.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3234>
0780e31581