Fix media_position for cast component (#8452)

* Make it available during state paused.

* Don't adjust for media_position_updated_at. I.e. do as vlc, sonos etc
  so that returned position is the position at the time of
  media_position_updated_at, not now.

homeassistant/components/media_player/cast.py

@@ -234,18 +234,13 @@ class CastDevice(MediaPlayerDevice):
     @property
     def media_position(self):
         """Position of current playing media in seconds."""
-        if self.media_status is None or self.media_status_received is None or \
+        if self.media_status is None or \
                 not (self.media_status.player_is_playing or
+                     self.media_status.player_is_paused or
                      self.media_status.player_is_idle):
             return None
 
-        position = self.media_status.current_time
-
-        if self.media_status.player_is_playing:
-            position += (dt_util.utcnow() -
-                         self.media_status_received).total_seconds()
-
-        return position
+        return self.media_status.current_time
 
     @property
     def media_position_updated_at(self):