MDEV-14968 On upgrade, InnoDB reports "started; log sequence number 0"

srv_prepare_to_delete_redo_log_files(): Initialize srv_start_lsn.

storage/innobase/srv/srv0start.cc

@@ -1446,6 +1446,7 @@ srv_prepare_to_delete_redo_log_files(
 			     << " bytes; LSN=" << flushed_lsn;
 		}
 
+		srv_start_lsn = flushed_lsn;
 		/* Flush the old log files. */
 		log_mutex_exit();