Make get_chat_members work with basic groups

pyrogram/client/methods/chats/get_chat_members.py

@@ -36,6 +36,17 @@ class GetChatMembers(BaseClient):
                          limit: int = 200,
                          query: str = "",
                          filter: str = Filters.ALL):
+        peer = self.resolve_peer(chat_id)
+
+        if isinstance(peer, types.InputPeerChat):
+            return utils.parse_chat_members(
+                self.send(
+                    functions.messages.GetFullChat(
+                        peer.chat_id
+                    )
+                )
+            )
+        elif isinstance(peer, types.InputPeerChannel):
             filter = filter.lower()
 
             if filter == Filters.ALL:
@@ -56,7 +67,7 @@ class GetChatMembers(BaseClient):
             return utils.parse_chat_members(
                 self.send(
                     functions.channels.GetParticipants(
-                    channel=self.resolve_peer(chat_id),
+                        channel=peer,
                         filter=filter,
                         offset=offset,
                         limit=limit,
@@ -64,3 +75,5 @@ class GetChatMembers(BaseClient):
                     )
                 )
             )
+        else:
+            raise ValueError("The chat_id \"{}\" belongs to a user".format(chat_id))