Fix handling of untranslated nodes

When building caja-actions package, UAF can happen in itstools, which is fixed by an upstream PR that hasn't been merged since almost two years ago. As upstream is inactive, I suggest we integrate that PR here. This makes the caja-actions package more reproducible.

• https://reproducible.archlinux.org/api/v0/builds/727962/log
• https://archriscv.felixc.at/.status/log.htm?url=logs/caja-actions/caja-actions-1.28.0-3.log

Link: https://github.com/itstool/itstool/pull/47