testcontroller: Fix crash when unplugging a controller while calibrating gyro

test/testcontroller.c

@@ -2208,9 +2208,9 @@ SDL_AppResult SDLCALL SDL_AppEvent(void *appstate, SDL_Event *event)
         }
 
         if (display_mode == CONTROLLER_MODE_TESTING) {
-            if (GamepadButtonContains(GetGyroResetButton(gyro_elements), event->button.x, event->button.y)) {
+            if (controller && GamepadButtonContains(GetGyroResetButton(gyro_elements), event->button.x, event->button.y)) {
                 ResetGyroOrientation(controller->imu_state);
-            } else if (GamepadButtonContains(GetGyroCalibrateButton(gyro_elements), event->button.x, event->button.y)) {
+            } else if (controller && GamepadButtonContains(GetGyroCalibrateButton(gyro_elements), event->button.x, event->button.y)) {
                 BeginNoiseCalibrationPhase(controller->imu_state);
             } else if (GamepadButtonContains(setup_mapping_button, event->button.x, event->button.y)) {
                 SetDisplayMode(CONTROLLER_MODE_BINDING);