Don't even offer the possibility to match using window role if the window

doesn't have it set.

svn path=/trunk/kdebase/kwin/; revision=334156

kcmkwin/kwinrules/detectwidget.cpp

@@ -98,6 +98,7 @@ void DetectDialog::executeDialog()
         };
     widget->class_label->setText( wmclass_class + " (" + wmclass_name + ' ' + wmclass_class + ")" );
     widget->role_label->setText( role );
+    widget->use_role->setEnabled( !role.isEmpty());
     if( type == NET::Unknown )
         widget->type_label->setText( i18n( "Unknown - will be treated as Normal Window" ));
     else