Fix LED interface crash if not implemented.

libretro.cpp

@@ -4887,7 +4887,7 @@ void retro_set_environment(retro_environment_t cb)
    if (environ_cb(RETRO_ENVIRONMENT_GET_VFS_INTERFACE, &vfs_iface_info))
 	   filestream_vfs_init(&vfs_iface_info);
 
-   environ_cb(RETRO_ENVIRONMENT_GET_LED_INTERFACE, &led_interface);
+  if(environ_cb(RETRO_ENVIRONMENT_GET_LED_INTERFACE, &led_interface))
    if (led_interface.set_led_state && !led_state_cb)
       led_state_cb = led_interface.set_led_state;