StudioWelcome: Fix crash

Check if a project does actually exist.

Task-number: QDS-3309
Change-Id: I59beff2637bbe80175dd223d6f574ea3886d95c5
Reviewed-by: Aleksei German <aleksei.german@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/studiowelcome/studiowelcomeplugin.cpp

@@ -163,6 +163,7 @@ public:
     {
         const QString projectFile = data(index(row, 0),
                                          ProjectModel::FilePathRole).toString();
+        if (QFileInfo::exists(projectFile))
             ProjectExplorer::ProjectExplorerPlugin::openProjectWelcomePage(projectFile);
     }