QmlDesigner: Add missing return

Task-number: QDS-9739
Change-Id: I4b48aaa72a906954ceb96b71e2b20efb76ac3d42
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qmldesigner/qmldesignerexternaldependencies.cpp

@@ -239,6 +239,8 @@ QStringList ExternalDependencies::modulePaths() const
 
         for (const QString &modulePath : qmlBuildSystem->customImportPaths())
             modulePaths.append(project->projectDirectory().pathAppended(modulePath).toString());
+
+        return modulePaths;
     }
 
     return {};