Restore panel config on containment switch

Summary:
::restore uses ::config which changes depending on the containment used.

calling positionPanel before restoring, means we're loading
garbage values. This was hidden as location was set just after which
did call restore().

Saves one incorrect resize.

Test Plan:
qDebug + starting plasmashell

Reviewers:
Marco Martin

Subscribers:

shell/panelview.cpp

@@ -1024,7 +1024,7 @@ void PanelView::themeChanged()
 
 void PanelView::containmentChanged()
 {
-    positionPanel();
+    restore();
     connect(containment(), SIGNAL(statusChanged(Plasma::Types::ItemStatus)), SLOT(statusChanged(Plasma::Types::ItemStatus)));
     connect(containment(), &Plasma::Applet::appletDeleted, this, [this] {
         //containment()->destroyed() is true only when the user deleted it