install/54313: sysinst terminates with "Window too short"

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         54313
>Category:       install
>Synopsis:       sysinst terminates with "Window too short"
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jun 20 07:00:00 +0000 2019
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date 2019.06.20.00.52.05
>Organization:

>Environment:
System: NetBSD
Architecture: i386
Machine: i386
>Description:

The latest install attempt on the TNF i386 testbed failed as sysinst 
exited with the error message

  Window too short (m->h -2, m->numopts 6, exithadd 1, y 23, max_lines 25, hadd 4) for menu "NetBSD-8.99.46 Install System"
  sysinst terminated.

Full log at

  http://releng.netbsd.org/b5reports/i386/commits-2019.06.html#2019.06.20.00.52.05

This is a new regression; installation worked as recently as
2019.06.19.16.14.07.

>How-To-Repeat:

>Fix: