Check if member is in list for GUILD_MEMBER_REMOVE.

discord/client.py

@@ -308,6 +308,7 @@ class ConnectionState(object):
         if server is not None:
             user_id = data['user']['id']
             member = utils.find(lambda m: m.id == user_id, server.members)
+            if member in server.members:
                 server.members.remove(member)
                 self.dispatch('member_remove', member)