By pushing a sentinel/dummy buffer on the input buffer fifo
when the output needs reconfiguring, we avoid deadlocks on
HTC Sensation, where the input buffers aren't returned to
the caller until the decoder has been reconfigured.

Since all input buffers can be used up before the reconfigure event
is received, this earlier led to a deadlock where the decoder
waited for the caller to reconfigure it (as a response to the
reconfigure event), while the caller waited for an input buffer
to be freed to put the next input packet into.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>