Start application service stream token tracking from 1 (#12193)

Co-authored-by: Erik Johnston <erik@matrix.org>

synapse/storage/databases/main/appservice.py

@@ -446,7 +446,8 @@ class ApplicationServiceTransactionWorkerStore(
             )
             last_stream_id = txn.fetchone()
             if last_stream_id is None or last_stream_id[0] is None:  # no row exists
-                return 0
+                # Stream tokens always start from 1, to avoid foot guns around `0` being falsey.
+                return 1
             else:
                 return int(last_stream_id[0])