Fixed potential bug with unset application id...

Fixed potential bug with unset application id https://honk.sigxcpu.org/con/GTK__and_the_application_id.html

src/gui-window.c

@@ -307,6 +307,7 @@ update_moodle_index (GuiWindow *self)
 static void
 gui_window_init (GuiWindow *self)
 {
+  g_set_prgname(APP_NAME);
   self->course_count = 0;
   self->dialog = NULL;
   gtk_widget_init_template (GTK_WIDGET (self));