Segfault when generating a UFO from a font with design size

[mf2vec-dev]

I ran into a segmentation fault when saving a font as UFO. I was able to isolate the problem and it is somehow caused by the design size.

Steps to reproduce

Run the following Python script

import fontforge
f = fontforge.font()
f.design_size = 10
f.generate('test.ufo')

Note: This does not seem to be related to Python. FontForge also crashes when generating the UFO using the GUI.

Actual behaviour

Segmentation fault (core dumped)

Expected behaviour

FontForge should not crash and the UFO should be generated.

FontForge version and OS

FontForge: 20230101 git:986f919997215865571d9d7524b457c5c7119cf6

Ubuntu 22.04.4 LTS