protect access to toolbox, when used with containments that don't create one or turn theirs off

BUG:179909

svn path=/trunk/KDE/kdelibs/; revision=907205

containment.cpp

@@ -1597,12 +1597,14 @@ void ContainmentPrivate::containmentConstraintsEvent(Plasma::Constraints constra
             a->updateConstraints(ImmutableConstraint);
         }
 
+        if (toolBox) {
             if (type == Containment::PanelContainment || type == Containment::CustomPanelContainment) {
                 toolBox->setVisible(unlocked);
             } else {
                 toolBox->setIsMovable(unlocked);
             }
         }
+    }
 
     if (constraints & Plasma::FormFactorConstraint) {
         if (toolBox) {