gui: exits gracefully

Software/PC_Application/main.cpp

@@ -17,6 +17,7 @@ static AppWindow *window;
 void sig_handler(int s) {
     Q_UNUSED(s)
     window->close();
+    app->quit();
 }
 
 int main(int argc, char *argv[]) {
@@ -36,6 +37,6 @@ int main(int argc, char *argv[]) {
     app = new QApplication(argc, argv_ext);
     window = new AppWindow;
     signal(SIGINT, sig_handler);
-    app->exec();
-    return 0;
+    auto rc = app->exec();
+    return rc;
 }