The _ToolbarPalette does get passed the invoker on
initialisation. But we do create the PaletteWindowWidget
later. We do attach the invoker to the widget when calling
_setup_widget that is why it was still working without that
patch.
This patch prevents the traceback that we had because of not
having a widget at this point.
Signed-off-by: Simon Schampijer <simon@laptop.org>
Tested-by: Manuel Quiñones <manuq@laptop.org>