browser-plugin: Correct check for checking the hostname/protocol

While it's extremely unlikely that document.location would not be an
object in the browser setting, this check is incorrect and we could
possibly crash an NPAPI host if this is the case.

https://bugzilla.gnome.org/show_bug.cgi?id=670489

browser-plugin/browser-plugin.c

@@ -104,7 +104,7 @@ check_origin_and_protocol (NPP instance)
                           &location))
     goto out;
 
-  if (!NPVARIANT_IS_OBJECT (document))
+  if (!NPVARIANT_IS_OBJECT (location))
     goto out;
 
   hostname = get_string_property (instance,