CppTools: Save some stats by using correct include paths

..while initial parsing.

Change-Id: I202da3f4f9e445a28e9726352fc005488efe2893
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cppmodelmanager.cpp

@@ -802,6 +802,7 @@ ProjectPart::Ptr CppModelManager::projectPartForProjectFile(const QString &proje
 
 QList<ProjectPart::Ptr> CppModelManager::projectPart(const QString &fileName) const
 {
+    QMutexLocker locker(&m_projectMutex);
     return m_fileToProjectParts.value(fileName);
 }