QmlDesigner.PropertyEditor: Crash fix

Fixing infinite loop in java script.

Task-number: QTCREATORBUG-16573
Change-Id: I490d8b85635b7209f7923f9c8341bf77962c57b6
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>

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

@@ -43,6 +43,8 @@ Controls.ComboBox {
 
     signal valueFromBackendChanged
 
+    property bool block: false
+
     ColorLogic {
         id: colorLogic
         backendValue: comboBox.backendValue
@@ -52,6 +54,11 @@ Controls.ComboBox {
 
         function invalidate() {
 
+            if (block)
+                return
+
+            block = true
+
             if (manualMapping) {
                 valueFromBackendChanged();
             } else if (!comboBox.useInteger) {
@@ -72,6 +79,8 @@ Controls.ComboBox {
                 if (comboBox.currentIndex !== backendValue.value)
                     comboBox.currentIndex = backendValue.value
             }
+
+            block = false
         }
     }