install/56228: extended partitioning segfaults when saving changes

[emily@ingalls.rocks]

>Number:         56228
>Category:       install
>Synopsis:       extended partitioning segfaults when saving changes
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jun 01 20:30:00 +0000 2021
>Originator:     emily
>Release:        9.2
>Organization:
>Environment:
N/A
>Description:
attempting to use the extended partitioner crashes the installer when saving or finishing partitioning.

this is tested with the installer for three different platforms: netbsd/i386 on a 486 machine with a single ide drive, netbsd/mac68k on a quadra 700 with a single scsi drive, and netbsd/vax on a vaxstation m38 with two scsi drives. the issue prevents the use of the extended partitioner for installation.
>How-To-Repeat:
enter the extended partitioner in the installer, and then save changes. whether or not any changes were made does not seem to change the result.
>Fix: