Prevent sending empty RTCP packet.

Review URL: http://webrtc-codereview.appspot.com/331009

git-svn-id: http://webrtc.googlecode.com/svn/trunk@1277 4adac7df-926f-26a2-2b94-8c16560cd09d

src/modules/rtp_rtcp/source/rtcp_sender.cc

@@ -2010,7 +2010,11 @@ RTCPSender::SendRTCP(const WebRtc_UWord32 packetTypeFlags,
             }
         }
     }while (false);
-
+    // Sanity don't send empty packets.
+    if (pos == 0)
+    {
+        return -1;
+    }
     return SendToNetwork(rtcpbuffer, (WebRtc_UWord16)pos);
 }