bug 1205540 make source stream available during RemoveInput r=padenot

--HG--
extra : rebase_source : f9b4e488e52eb3717808c0efbaf5c0815627c8f0

dom/media/MediaStreamGraph.cpp

@@ -2365,8 +2365,8 @@ MediaInputPort::Disconnect()
     return;
 
   mSource->RemoveConsumer(this);
-  mSource = nullptr;
   mDest->RemoveInput(this);
+  mSource = nullptr;
   mDest = nullptr;
 
   GraphImpl()->SetStreamOrderDirty();