Bug 1164582 - Report an error when the appdata portion of a webrtc msid is missing. r=mt

--HG--
extra : transplant_source : %85%F8H%F3%C1N6%BD%9E%BC%D3o%27%A3Z%FE%8A%1BL%17

media/webrtc/signaling/src/jsep/JsepSessionImpl.cpp

@@ -610,6 +610,11 @@ JsepSessionImpl::GetIdsFromMsid(const Sdp& sdp,
 
   for (auto i = allMsids.begin(); i != allMsids.end(); ++i) {
     if (allMsidsAreWebrtc || webrtcMsids.count(i->identifier)) {
+      if (i->appdata.empty()) {
+        JSEP_SET_ERROR("Invalid webrtc msid at level " << msection.GetLevel()
+                       << ": Missing track id.");
+        return NS_ERROR_INVALID_ARG;
+      }
       if (!found) {
         *streamId = i->identifier;
         *trackId = i->appdata;