Fixes a NullPointerException which prevented establishing calls. Reported by Boris Grozev.

src/net/java/sip/communicator/service/protocol/media/CallPeerMediaHandler.java

@@ -1002,6 +1002,10 @@ private void callPropertyChange(PropertyChangeEvent event)
             for (MediaType mediaType : MediaType.values())
             {
                 MediaStream stream = getStream(mediaType);
+
+                if (stream == null)
+                    continue;
+
                 MediaDevice oldDevice = stream.getDevice();
 
                 if (oldDevice != null)