CppTools: Avoid using old incomplete semantic info document

Task-number: QTCREATORBUG-11367
Change-Id: I8b02c30a43a57c547bc07d796f4b29725beca793
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/cpptools/cpptoolseditorsupport.cpp

@@ -541,6 +541,7 @@ void CppEditorSupport::recalculateSemanticInfoNow(const SemanticInfo::Source &so
         semanticInfo.forced = source.force;
 
         if (!source.force
+                && m_lastSemanticInfo.complete
                 && m_lastSemanticInfo.revision == source.revision
                 && m_lastSemanticInfo.doc
                 && m_lastSemanticInfo.doc->translationUnit()->ast()