ensure the groups() list doesn't contain null pointer (could fix some bugs, but tendds to generate backtraces not directly obvious)

svn path=/trunk/KDE/kdelibs/; revision=1127890

extenders/extender.cpp

@@ -284,9 +284,11 @@ QList<ExtenderGroup*> Extender::groups() const
     QList<ExtenderGroup*> result;
     foreach (ExtenderItem *item, d->attachedExtenderItems) {
         if (item->isGroup() && !result.contains(item->group())) {
+           if (item->group()) {
                result.append(item->group());
            }
         }
+    }
     return result;
 }