fix crash from wrong FrameSvgItem initialization

--enable shadows by default on startup otherwise
the FrameSvgItem sets is imagepath to "" and that
can create a crash during loading/unloading a
layout

app/dock/dockview.cpp

@@ -134,6 +134,9 @@ DockView::~DockView()
 
     qDebug() << "dock view deleting...";
     rootContext()->setContextProperty(QStringLiteral("dock"), nullptr);
+    rootContext()->setContextProperty(QStringLiteral("themeExtended"), nullptr);
+    rootContext()->setContextProperty(QStringLiteral("universalSettings"), nullptr);
+    rootContext()->setContextProperty(QStringLiteral("layoutManager"), nullptr);
 
     //! this disconnect does not free up connections correctly when
     //! dockView is deleted. A crash for this example is the following:

containment/package/contents/ui/PanelBox.qml

@@ -155,7 +155,8 @@ Item{
 
         enabledBorders: dock && dock.effects ? dock.effects.enabledBorders : PlasmaCore.FrameSvg.NoBorder
 
-        property bool themeHasShadow: themeExtended ? themeExtended.hasShadow : false
+        //! set true by default in order to avoid crash on startup because imagePath is set to ""
+        readonly property bool themeHasShadow: themeExtended ? themeExtended.hasShadow : true
 
         Behavior on opacity {
             enabled: Latte.WindowSystem.compositingActive

containment/package/contents/ui/main.qml

@@ -346,10 +346,10 @@ DragDrop.DropArea {
     property Item latteApplet
     property Item parabolicManager: _parabolicManager
 
-    property QtObject dock
-    property QtObject themeExtended
-    property QtObject universalSettings
-    property QtObject universalLayoutManager
+    property QtObject dock: null
+    property QtObject themeExtended: null
+    property QtObject universalSettings: null
+    property QtObject universalLayoutManager: null
     property QtObject dockManagedLayout: dock && dock.managedLayout ? dock.managedLayout : null
 
     // TO BE DELETED, if not needed: property int counter:0;