Fix .get_dialogs() failing due to IDs being marked

Also removed utils.find_user_or_chat to prevent this from
happening again. Using a dict {marked_id: entity} is better.

telethon/telegram_client.py

@@ -338,9 +338,8 @@ class TelegramClient(TelegramBareClient):
                 break
 
             offset_date = r.messages[-1].date
-            offset_peer = utils.find_user_or_chat(
-                r.dialogs[-1].peer, entities, entities
-            )
+            offset_peer = entities[
+                utils.get_peer_id(r.dialogs[-1].peer, add_mark=True)]
             offset_id = r.messages[-1].id & 4294967296  # Telegram/danog magic
 
         dialogs = UserList(dialogs.values())

telethon/utils.py

@@ -386,28 +386,6 @@ def resolve_id(marked_id):
     return -marked_id, PeerChat
 
 
-def find_user_or_chat(peer, users, chats):
-    """Finds the corresponding user or chat given a peer.
-       Returns None if it was not found"""
-    if isinstance(peer, PeerUser):
-        peer, where = peer.user_id, users
-    else:
-        where = chats
-        if isinstance(peer, PeerChat):
-            peer = peer.chat_id
-        elif isinstance(peer, PeerChannel):
-            peer = peer.channel_id
-
-    if isinstance(peer, int):
-        if isinstance(where, dict):
-            return where.get(peer)
-        else:
-            try:
-                return next(x for x in where if x.id == peer)
-            except StopIteration:
-                pass
-
-
 def get_appropriated_part_size(file_size):
     """Gets the appropriated part size when uploading or downloading files,
        given an initial file size"""