gst/gstbin.c: Fix a big bug that was breaking pipelines like sinesrc ! { queue !...

gst/gstbin.c: Fix a big bug that was breaking pipelines like sinesrc ! { queue ! osssink } when an error was thrown b...

Original commit message from CVS:
2004-02-15  Julien MOUTTE  <julien@moutte.net>

* gst/gstbin.c: (gst_bin_change_state), (gst_bin_iterate): Fix a big
bug that was breaking pipelines like sinesrc ! { queue ! osssink } when
an error was thrown by osssink. Basically a state change failure for
an element in a different scheduling group was considered as successfull        , which means that caps nego was going on and weird stuff happened. Like        i wrote in the comment there, if someone want to revert that please
drop me a mail explaining why because i really see no point in keeping
that broken behaviour there.
* gst/gstqueue.c: (gst_queue_get): Add a safety check as the queue CAN
be empty, we then return NULL which will trigger a nice error when
pulling from the pad.