Don't call env cb if it's NULL

src/conio/retro.c

@@ -272,9 +272,11 @@ retro_set_environment(retro_environment_t cb)
 {
 	env_cb = cb;
 	retro_set = true;
+	if (cb) {
 		cb(RETRO_ENVIRONMENT_SET_PIXEL_FORMAT, &rpf);
 		cb(RETRO_ENVIRONMENT_SET_KEYBOARD_CALLBACK, &rkc);
 		cb(RETRO_ENVIRONMENT_SET_SUPPORT_NO_GAME, &no_game);
+	}
 	// RETRO_ENVIRONMENT_SET_FRAME_TIME_CALLBACK
 	// RETRO_ENVIRONMENT_SET_AUDIO_CALLBACK
 }