install/60067: Segfault on disklabel partition from outside the MBR bounds

["ja%sdomi.pl@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60067
>Category:       install
>Synopsis:       Segfault on disklabel partition from outside the MBR bounds
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Mar 09 21:40:00 +0000 2026
>Originator:     dmi
>Release:        11.0 RC2
>Organization:
>Environment:
qemu-system-i386 -cdrom ~/NetBSD-11.0_RC2-i386.iso -m 64M -drive format=raw,file=/dev/sdf -boot d -accel kvm
>Description:
Adding a user-defined disklabel partition in the installer causes UB if the "start" field is lower than the wedge start; In my case, on a 4GB drive I had created two MBR partitions:

- 64MB DOSFS
- rest of the disk NetBSD

I wanted to get the first MBR partition visible in the wedge to mount it as /boot; However, upon entering start: 0MB, size: 64MB, and accepting the settings, the main menu of the disklabel step would get mangled (repeated options / duplicate partitions) or the program would crash ( https://f.sakamoto.pl/IwIPMuDg.png )
>How-To-Repeat:
1. Boot up the installer in QEMU
2. Create MBR as described above
3. Add a disklabel part with a start of "0MB"
4. x, enter
5. Observe as the universe crumbles
>Fix: