audioringbuffer: don't attempt to reorder position-less channels

audioringbuffer: don't attempt to reorder position-less channels

As said in its doc GST_AUDIO_CHANNEL_POSITION_NONE is meant to be used
for "position-less channels, e.g. from a sound card that records 1024
channels; mutually exclusive with any other channel position".

But at the moment using such positions would raise a
'g_return_if_reached' warning as gst_audio_get_channel_reorder_map()
would reject it.

Fix this by preventing any attempt to reorder in such case as that's not
what we want anyway.

https://bugzilla.gnome.org/show_bug.cgi?id=763799