fix: avoid panic when client is confused about rooms

src/database/key_value/rooms/timeline.rs

@@ -330,7 +330,7 @@ fn count_to_id(
         .rooms
         .short
         .get_shortroomid(room_id)?
-        .expect("room exists")
+        .ok_or_else(|| Error::bad_database("Looked for bad shortroomid in timeline"))?
         .to_be_bytes()
         .to_vec();
     let mut pdu_id = prefix.clone();