175920, Null window references are not in the content area.

r=bugs4hj@netscape.net
sr=bryner@netscape.com
a=roc+moz@cs.cmu.edu

xpfe/communicator/resources/content/contentAreaUtils.js

@@ -42,6 +42,9 @@
  **/
 function isContentFrame(aFocusedWindow)
 {
+  if (!aFocusedWindow)
+    return false;
+
   var focusedTop = Components.lookupMethod(aFocusedWindow, 'top')
                              .call(aFocusedWindow);