Bugfixes in chat.py (#411)

- Fixed this bug: https://t.me/pyrogramchat/169553 (which was caused because pyrogram trying to parse linked_chat even if it was None).

- Fixed another related bug (which was caused because pyrogram trying to get linked_chat_id even with basic groups causing an AttributeError).

pyrogram/client/types/user_and_chats/chat.py

@@ -252,6 +252,7 @@ class Chat(Object):
                 if full_chat.id == c.id:
                     chat = c
                     
+                if isinstance(chat_full, types.ChannelFull):
                     if full_chat.linked_chat_id == c.id:
                         linked_chat = c
 
@@ -268,6 +269,7 @@ class Chat(Object):
                 # TODO: Add StickerSet type
                 parsed_chat.can_set_sticker_set = full_chat.can_set_stickers
                 parsed_chat.sticker_set_name = getattr(full_chat.stickerset, "short_name", None)
+                if linked_chat:
                     parsed_chat.linked_chat = Chat._parse_channel_chat(client, linked_chat)
 
             if full_chat.pinned_msg_id: