qt: Don't resize non-existent monitors

src/qt/qt_main.cpp

@@ -290,6 +290,7 @@ int main(int argc, char* argv[]) {
     {
         /* If needed, handle a screen resize. */
         for (int i = 0; i < MONITORS_NUM; i++) {
+            if (!monitors[i].target_buffer) continue;
             if (!atomic_flag_test_and_set(&doresize_monitors[i]) && !video_fullscreen && !is_quit) {
                 if (vid_resize & 2)
                     plat_resize_monitor(fixed_size_x, fixed_size_y, i);

src/qt/qt_mainwindow.cpp

@@ -1617,7 +1617,7 @@ static void update_scaled_checkboxes(Ui::MainWindow* ui, QAction* selected) {
     device_force_redraw();
     video_force_resize_set(1);
     for (int i = 0; i < MONITORS_NUM; i++)
-        atomic_flag_clear(&doresize_monitors[i]);
+        if (monitors[i].target_buffer) atomic_flag_clear(&doresize_monitors[i]);
     config_save();
 }