Handle case when no valid entity is set yet

[ikaruswill]

When creating a new card using the default options without a valid entity_id specified, the card fails to render with errors in console.

Default options:

name: Xiaomi Fan
platform: default
entity: fan.fan
disable_animation: false
use_standard_speeds: true
force_sleep_mode_support: false
hide_led_button: false
type: custom:fan-xiaomi

Console:

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'device_id')
    at FanXiaomi.configureAsync