... property name validation.
GLib tightened its GParamSpec name validation, as it used to only check
that the first letter was a letter, which triggered this issue, though
the crash could have also happened with the former lax rules too (commit
30e630c9df792cf36cdb1cceb3daefbde1dc898a).
I opened a merge request in GLib to make the validation code into a
public function. In the meantime, let's just copy-paste the validation
code into ours and when a plug-in attempts to create a procedure with
invalid parameter or return value names, GIMP will just output an error
and refuse to install the procedure instead of crashing.
See: https://gitlab.gnome.org/GNOME/glib/merge_requests/1302
4550fc1bfa