disable inconsistent when setting true/false

Change-Id: Ib612e7f38c7a1a638d69af2a6d26f1293fe0c8da
Reviewed-on: https://gerrit.libreoffice.org/55011Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/unx/gtk3/gtk3gtkinst.cxx

@@ -2692,6 +2692,7 @@ public:
     virtual void set_active(bool active) override
     {
         disable_notify_events();
+        gtk_toggle_button_set_inconsistent(m_pToggleButton, false);
         gtk_toggle_button_set_active(m_pToggleButton, active);
         enable_notify_events();
     }