QmlDesigner: Workaround for regression in Qt

Editing finished is emitted, when we show an error dialog,
and the TextFiled looses focus. Even if the value did not change.

This triggers a second error dialog and hangs on macOS.
This is a regression from Qt 5.11 to Qt 5.12.x.

The workaround is to check for the value change manually.

Task-number: QDS-519
Change-Id: Ie8a3f342bc0b81941d07773d52947ad76ae27205
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

share/qtcreator/qmldesigner/statesEditorQmlSources/StatesDelegate.qml

@@ -154,11 +154,17 @@ Rectangle {
                 __panel.visible = false
         }
 
-        onEditingFinished: {
-            if (text != delegateStateName)
-                statesEditorModel.renameState(internalNodeId, text)
-        }
+        property string oldValue
 
+        onEditingFinished: {
+            if (stateNameField.oldValue === stateNameField.text)
+                return
+
+            stateNameField.oldValue = stateNameField.text
+
+            if (stateNameField.text != delegateStateName)
+                statesEditorModel.renameState(internalNodeId, stateNameField.text)
+        }
     }
 
     Item {