QmlJSEditor: Do not allow child items for states

Task-number: QTCREATORBUG-13003
Change-Id: I30bcee12803d2b3af804625ffdf417316e3d6c32
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>

src/libs/qmljs/qmljsstaticanalysismessage.cpp

@@ -235,6 +235,8 @@ StaticAnalysisMessages::StaticAnalysisMessages()
             tr("States are only supported in the root item in a Qt Quick UI form."));
     newMsg(ErrReferenceToParentItemNotSupportedInQmlUi, Error,
             tr("Referencing the parent of the root item is not supported in a Qt Quick UI form."));
+    newMsg(StateCannotHaveChildItem, Error,
+            tr("A State cannot have a child item (%1)."), 1);
 }
 
 } // anonymous namespace