fontchooser: Make sure the tweak button is updated

This was showing up as tweak buttons being visible
when they should not. The code probably relied on
widgets being hidden by default (as they were in
GTK3).

gtk/gtkfontchooserdialog.c

@@ -183,6 +183,8 @@ setup_tweak_button (GtkFontChooserDialog *dialog)
       gtk_header_bar_pack_end (GTK_HEADER_BAR (header), button);
 
       dialog->tweak_button = button;
+
+      update_tweak_button (dialog);
     }
 }