fix regressions introduced by 29582de6 (fix for SL#1742)

GTK pops down the palette before it invokes the actions on the
menu item. We need to postpone destruction of the palette until
after all signals have propagated from the menu item to the
palette owner.

Symptoms included the "View Details" palette menu item in the Journal list
view not working.

Signed-off-by: Sascha Silbe <silbe@activitycentral.com>
Acked-by: Simon Schampijer <simon@laptop.org>

src/sugar/graphics/palettewindow.py

@@ -643,7 +643,13 @@ class Invoker(gobject.GObject):
         if self._palette is not None:
             self._palette.popdown(immediate=True)
             self._palette.props.invoker = None
-            self._palette.destroy()
+            # GTK pops down the palette before it invokes the actions on the
+            # menu item. We need to postpone destruction of the palette until
+            # after all signals have propagated from the menu item to the
+            # palette owner.
+            gobject.idle_add(lambda old_palette=self._palette:
+                             old_palette.destroy(),
+                             priority=gobject.PRIORITY_LOW)
 
         self._palette = palette