Add break condition in cleanup script

cleanup.py

@@ -36,6 +36,10 @@ for i in range(5):  # default: check 5 batches of 40 posts
     # get next batch of posts
     last_posts = mastodon.account_statuses(getenv("MASTODON_USER_ID"), exclude_replies=True, max_id=id_oldest_of_last_posts, limit=40)
 
+    # break if there are no more posts
+    if len(last_posts) == 0:
+        break
+
     # delete all old posts of the current batch
     for submission in last_posts:
         # if post has no favorites, boosts or replies, delete it