fix aiohttp InvalidURL exception when fetching media player image (#15572)

* fix aiohttp InvalidURL exception when fetching media player image

The first call for the HA proxy (`/api/media_player_proxy/media_player.kodi?token=...&cache=...`)
is receiving relative urls that are failing, this is a simple fix to precede the base_url when hostname is None.

* fix import location and sort stdlib imports

homeassistant/components/media_player/__init__.py

@@ -6,12 +6,13 @@ https://home-assistant.io/components/media_player/
 """
 import asyncio
 import base64
+import collections
 from datetime import timedelta
 import functools as ft
-import collections
 import hashlib
 import logging
 from random import SystemRandom
+from urllib.parse import urlparse
 
 from aiohttp import web
 from aiohttp.hdrs import CONTENT_TYPE, CACHE_CONTROL
@@ -956,6 +957,9 @@ async def _async_fetch_image(hass, url):
     cache_images = ENTITY_IMAGE_CACHE[CACHE_IMAGES]
     cache_maxsize = ENTITY_IMAGE_CACHE[CACHE_MAXSIZE]
 
+    if urlparse(url).hostname is None:
+        url = hass.config.api.base_url + url
+
     if url not in cache_images:
         cache_images[url] = {CACHE_LOCK: asyncio.Lock(loop=hass.loop)}