2004-07-06  Michael Natterer  <mitch@gimp.org>

	* app/widgets/gimppreviewrenderer.c
	(gimp_preview_renderer_set_viewable): queue an idle update when
	setting the viewable to NULL so the view gets cleared correctly.

	(gimp_preview_renderer_idle_update): call
	gimp_preview_renderer_update() even if renderer->viewable is NULL
	so clearing the viewable gets propagated to the GUI.

	Moved clearing the viewable and removing the idle from
	GObject::finalize() to GObject::dispose() because calling
	set_viewable() with a NULL viewable triggers typechecking casts
	and queuing idle functions, which is not nice in finalize().