mpegtspacketizer: be more tolerant when parsing the adaptation field

mpegtspacketizer: be more tolerant when parsing the adaptation field

According to the specification, the adaptation field length must be 183 if
there is no payload data and < 183 if the packet contains an adaptation
field and payload data.

Unfortunately some payloaders always set the flag for payload data, even if
the adaptation field length is 183.

Don't return with an error in this case. Clear the payload data flag
instead and parse the adaptation field as usual. This avoids visual
artefacts for such streams.