QmlDesigner: Ensure not every type is valid

Change-Id: I192adf9703ceefe3d1178cdb1160e164ed46cbd9
Reviewed-by: Henning Gründl <henning.gruendl@qt.io>
(cherry picked from commit 8abb142fcb)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/plugins/qmldesigner/libs/designercore/metainfo/nodemetainfo.cpp

@@ -837,6 +837,7 @@ NodeMetaInfoPrivate::NodeMetaInfoPrivate(Model *model, TypeName type, int maj, i
 
                 m_objectValue = getObjectValue();
                 m_defaultPropertyName = context()->defaultPropertyName(objectValue).toUtf8();
+                if (m_objectValue)
                     m_isValid = true;
                 setupPrototypes();
             }