No timezone completion list in clock plugin properties window

On FreeBSD, when trying to type new timezone name in clock properties window, then no zone completion list show up. The root cause of this problem is that FreeBSD does not have "/usr/share/zoneinfo/posix/" directory, but timezone names are based on contents of this directory (https://gitlab.xfce.org/xfce/xfce4-panel/-/blob/master/plugins/clock/clock.c#L55).

I have tested it on FreeBSD 12.3 machine with Xfce4 panel 4.16.5.