void
g_list_free_full (GList *list,
                  GDestroyNotify free_func);

Convenience method, which frees all the memory used
by a GList, and calls free_func on every element's
data.

https://developer.gnome.org/glib/stable/glib-Doubly-Linked-Lists.html#g-list-free-full

Note that GTK+ sets a default title of _("About %s") on the dialog
window (where %s is replaced by the name of the application, but
in order to ensure proper translation of the title, applications
should set the title property explicitly when constructing a
GtkAboutDialog

https://developer.gnome.org/gtk3/stable/GtkAboutDialog.html

Also stop any other segfaults caused by failure of deprecated gtk_action_group_get_action to return the name of the active item. With GTK 3.23.0 cpufreq_popup_menu_set_active sends invalid name information for userspace governors

happens if build with -lcpupower and kernel 4.7+

```
cpufreq-monitor-libcpufreq.c: In function 'cpufreq_monitor_libcpufreq_run':
cpufreq-monitor-libcpufreq.c:117:7: warning: implicit declaration of function 'cpupower_is_cpu_online' [-Wimplicit-function-declaration]
   if (cpupower_is_cpu_online (cpu)) {
       ^~~~~~~~~~~~~~~~~~~~~~
```

Use a default "---" label until frequency values are found