fix blank space in preview window for single win

plasmoid/contents/ui/ToolTipDelegate2.qml

@@ -80,6 +80,33 @@ PlasmaExtras.ScrollArea {
             return isVerticalPanel ? contentItem.height > viewport.height : contentItem.width > viewport.width
         });
     }
+    Item{
+        anchors.fill: contentItem
+
+        DropArea {
+            id: dropMainArea
+            anchors.fill: contentItem
+            enabled: isGroup
+
+            preventStealing: true
+
+            property bool dragInside: false
+
+            property QtObject currentWindow
+
+            onDragLeave: {
+                windowsPreviewDlg.hide();
+            }
+
+            onDragMove: {
+                var current = groupTask.childAtPos(event.x, event.y);
+
+                if (current && currentWindow !== current && current.submodelIndex) {
+                    currentWindow = current;
+                    tasksModel.requestActivate(current.submodelIndex);
+                }
+            }
+        }
 
         MouseArea {
             id: contentItem
@@ -110,31 +137,6 @@ PlasmaExtras.ScrollArea {
                 return singleTask.containsMouse() || groupTask.containsMouse();
             }
 
-        DropArea {
-            id: dropMainArea
-            anchors.fill: contentItem
-            enabled: isGroup
-
-            preventStealing: true
-
-            property bool dragInside: false
-
-            property QtObject currentWindow
-
-            onDragLeave: {
-                windowsPreviewDlg.hide();
-            }
-
-            onDragMove: {
-                var current = groupTask.childAtPos(event.x, event.y);
-
-                if (current && currentWindow !== current && current.submodelIndex) {
-                    currentWindow = current;
-                    tasksModel.requestActivate(current.submodelIndex);
-                }
-            }
-        }
-
             ToolTipInstance {
                 id: singleTask
                 visible: !isGroup
@@ -190,4 +192,5 @@ PlasmaExtras.ScrollArea {
                 }
             }
         }
+    }
 }