Use deleteLater when called on a decoder error.

Since we cleanup the decoder itself, it can crash when the stack
unwinds back into the decoder code.  Similarly on a network error.

Change-Id: Ice36a3008359565f186406945973747b3134d296
Reviewed-by: Ling Hu <ling.hu@nokia.com>
(cherry picked from commit fb10bcf6cea520e1c43a77b6b88cf01ae9dc74ad)

src/multimedia/effects/qsamplecache_p.cpp

@@ -282,8 +282,8 @@ void QSample::release()
 // must be called locked.
 void QSample::cleanup()
 {
-    delete m_waveDecoder;
-    delete m_stream;
+    m_waveDecoder->deleteLater();
+    m_stream->deleteLater();
     m_waveDecoder = 0;
     m_stream = 0;
 }