Do not try to complete flush operation if stream has changed.

There is a problem when sound effect already has a sound loaded and
we try to load new sound with setSource().
When sampleReady() is called between emptyStream() and emptyComplete()
it unloads the current stream and creates a new stream.
As a result pulse audio crashed in emptyComplete() while calling
pa_operation_unref(pa_stream_cork(
m_pulseStream, 1, stream_cork_callback, m_ref->getRef()))
with the new m_pulseStream.

Change-Id: Idff4fe6037d3f3f116734dc0facabaafa3db14a2
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>
Reviewed-by: Ling Hu <ling.hu@nokia.com>

src/multimedia/audio/qsoundeffect_pulse_p.h

@@ -118,7 +118,7 @@ private Q_SLOTS:
     void underRun();
     void prepare();
     void streamReady();
-    void emptyComplete();
+    void emptyComplete(void *stream);
     void updateVolume();
     void updateMuted();