CppEditor: Catch another project pointer access from a thread

Amends 33108795d6.

Fixes: QTCREATORBUG-27044
Change-Id: I53d716355b0784841fd8d965c8af14fe321c33de
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cppeditor/projectinfo_test.cpp

@@ -60,8 +60,11 @@ public:
 
     const ProjectPartInfo choose()
     {
+        const Project * const project = projectMap.value(activeProject).get();
+        const Utils::FilePath projectFilePath = project ? project->projectFilePath()
+                                                        : Utils::FilePath();
         return chooser.choose(filePath, currentProjectPartInfo, preferredProjectPartId,
-                              projectMap.value(activeProject).get(),
+                              projectFilePath,
                               languagePreference, projectsChanged);
     }