playbin2: Fix decoder-sink compatibility check for raw audio/video formats

playbin2: Fix decoder-sink compatibility check for raw audio/video formats

If the sink supports raw audio/video, we first check
if the decoder could output any raw audio/video format
and assume it is compatible with the sink then. We don't
do a complete compatibility check here if converters
are plugged between the decoder and the sink because
the converters will convert between raw formats and
even if the decoder format is not supported by the decoder
a converter will convert it.

We assume here that the converters can convert between
any raw format.

Fixes bug #665120.