Fix plugin search with GLib 2.69.
Review Request #856 — Created July 30, 2021 and submitted
Named groups in
GRegexwith GLib 2.69 appear to return empty, not
NULLstrings, so handle that when running version comparison.
This is actually what GLib documents should happen, but I guess didn't work right before.
Compiled and ran tests on Fedora Rawhide with GLib 2.69.