Fix a bug with negative SSRCs for a stream, reported by Thomas Kuntz.

src/org/jitsi/impl/neomedia/MediaStreamImpl.java

@@ -175,7 +175,8 @@ else if (MediaDeviceSession.SSRC_LIST.equals(propertyName))
     /**
      * Our own SSRC identifier.
      */
-    private long localSourceID = new Random().nextInt();
+    private long localSourceID = Math.abs(new Random().nextLong())
+            % Integer.MAX_VALUE;
 
     /**
      * The list of CSRC IDs contributing to the media that this