Make sure that the defaultView exists before attempting to get at the...

Make sure that the defaultView exists before attempting to get at the computedStyle (makes it easier to hide items that don't have a view). Fixes #5619.

src/css.js

@@ -141,7 +141,13 @@ jQuery.extend({
 
 			name = name.replace( rupper, "-$1" ).toLowerCase();
 
-			var computedStyle = elem.ownerDocument.defaultView.getComputedStyle( elem, null );
+			var defaultView = elem.ownerDocument.defaultView;
+
+			if ( !defaultView ) {
+				return null;
+			}
+
+			var computedStyle = defaultView.getComputedStyle( elem, null );
 
 			if ( computedStyle ) {
 				ret = computedStyle.getPropertyValue( name );