Sometimes the vty switching has to be delayed; the vty
to be switched to is saved in sc->delayed_next_scr and
the actual switch is performed later. It was possible
to get into the endless loop when attempting to switch
to a closed vty (which is not allowed and beep-alerted
when attempted) and when the visual beep was in effect.
This caused sc->delayed_next_scr to never be reset and
endless attempts to switch to a closed vty and endless
visual beeping. How to repeat:

• boot into single-user
• run "kbdcontrol -b visual"
• quickly press Alt+F2 two times

PR: kern/68016
X-MFC after: 6.2-RELEASE