Fix visitor nit
Fix visitor nit

Summary: Probably will never matter, but this should have a byte swap check.

Reviewed By: ssj933

Differential Revision: D34469981

fbshipit-source-id: fdbc5913a96de8ef202968a3c2838536e3ff08d6

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex