Handle the case when default_send_as is None (#842)

* fix parsing send_as peer.

* Update chat.py

Co-authored-by: Dan <14043624+delivrance@users.noreply.github.com>

pyrogram/types/user_and_chats/chat.py

@@ -320,6 +320,7 @@ class Chat(Object):
 
                 default_send_as = full_chat.default_send_as
 
+                if default_send_as:
                     if isinstance(default_send_as, raw.types.PeerUser):
                         send_as_raw = users[default_send_as.user_id]
                     else: