Noissue - Fix some problems Firefox has with our injected code

inject.preload.js

Index: inject.preload.js
diff --git a/inject.preload.js b/inject.preload.js
index ce6912136372870d2e7c3510994e6e05c3198984..357f6dd4d24f5c3a9847898102c7a6b479c53067 100644
--- a/inject.preload.js
+++ b/inject.preload.js
@@ -174,8 +174,9 @@ function injected(eventName, injectedIntoContentWindow)
   {
     for (let name of properties)
     {
-      Object.defineProperty(dest, name,
-                            Object.getOwnPropertyDescriptor(src, name));
+      let descriptor = Object.getOwnPropertyDescriptor(src, name);
+      if (descriptor)
+        Object.defineProperty(dest, name, descriptor);
     }
   }
 
@@ -359,10 +360,15 @@ function injected(eventName, injectedIntoContentWindow)
       return WrappedRTCPeerConnection();
 
     let configuration = protectConfiguration(args[0]);
+
     // Since the old webkitRTCPeerConnection constructor takes an optional
     // second argument we need to take care to pass that through. Necessary
     // for older versions of Chrome such as 49.
-    let peerconnection = new RealRTCPeerConnection(configuration, args[1]);
+    let constraints = undefined;
+    if (args.length > 1)
+      constraints = args[1];
+
+    let peerconnection = new RealRTCPeerConnection(configuration, constraints);
     checkConfiguration(peerconnection, configuration);
     return peerconnection;
   }