QmlDesigner.PropertyEditor: Final fixes for gradient editing

We react to selection change now and keep the selection.

Change-Id: I847b8cf308277df92295822f9cd18ebb58cc2ba0
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

share/qtcreator/qmldesigner/propertyEditorQmlSources/HelperWidgets/GradientLine.qml

@@ -39,8 +39,13 @@ Item {
 
     property bool hasGradient: gradientModel.hasGradient
 
+
     property alias gradientPropertyName: gradientModel.gradientPropertyName
 
+    onHasGradientChanged: {
+        colorLine.invalidate()
+    }
+
     onCurrentColorChanged: {
         gradientModel.setColor(colorLine.selectedIndex, currentColor)
         colorLine.invalidate()
@@ -55,6 +60,14 @@ Item {
         gradientModel.deleteGradient()
     }
 
+    Connections {
+        target: modelNodeBackend
+        onSelectionChanged: {
+            colorLine.invalidate()
+            colorLine.select(0)
+        }
+    }
+
     Item {
         id: colorLine
         height: 80
@@ -283,6 +296,7 @@ Item {
                         }
                         parent.y = 20
                         colorLine.invalidate()
+                        colorLine.select(colorLine.selectedIndex)
                     }
                 }
             }