Created attachment 196718 [details] [review]
Prevent the demuxer from sending EOS when doing a flushing seek while in paused state

Create a pipeline similar to the following

filesrc ! matroskademux ! queue ! ...

Pause the pipeline and wait for it to preroll. Then do a flushing seek.
Sometimes this will result in the demuxer sending an EOS.

This is done from gst_matroska_demux_loop() because it gets a  
GST_FLOW_UNEXPECTED return value from the EBML-reader, from
gst_ebml_peek_id_length(). This function will always return GST_FLOW_UNEXPECTED
if the peek fails. No matter what the reason for the fail is.

For example, in the situation above (when the EOS is sent) the reason for the
peek failure is that the filesrc is flushing, and returns GST_FLOW_WRONG_STATE when the get_range function is called. But this never reaches the ebml reader,
which instead returns a GST_FLOW_UNEXPECTED.

I have attached a patch where I have changed the reader to return the correct 
value, i.e. the value that the peek function returns.