Fix stop sign page race condition with checkout

Fix stop sign page race condition with checkout

This would happen most often when retrieving multiple patrons at the same time
from patron search--the stop sign page would show but then get trampled by the
checkout interface, which normally loads first.

Signed-off-by: Jason Etheridge <jason@esilibrary.com>
Signed-off-by: Thomas Berezansky <tsbere@mvlc.org>