sipcall: fix getVideoReceiver

It was always returning nullptr

Change-Id: I122db004d63b7844b05589f7de596d50140a1795

src/sip/sipcall.h

@@ -152,7 +152,7 @@ public:
     {
         auto const& videoRtp = getVideoRtp();
         if (videoRtp)
-            videoRtp->getVideoReceive().get();
+            return videoRtp->getVideoReceive().get();
 
         return nullptr;
     }