Check for null as well as undefined in isBodyLoaded()

Review at http://gwt-code-reviews.appspot.com/1111801

Review by: conroy@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9239 8db76d5a-ed1c-0410-87a9-c151d255dfc7
diff --git a/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeTemplate.js b/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeTemplate.js
index d776b54..47a611d 100644
--- a/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeTemplate.js
+++ b/dev/core/src/com/google/gwt/core/linker/CrossSiteIframeTemplate.js
@@ -27,7 +27,7 @@
       // FF 3.5 and below does not have readyState, but it does allow us to
       // append to the body before it has finished loading, so we return whether
       // the body element exists.
-      return (typeof $doc.body != "undefined");
+      return (typeof $doc.body != "undefined" && $doc.body != null);
     }
     return (/loaded|complete/.test($doc.readyState));
   }