Fix undo and redo button dropdowns when no document open

Closes #29

TODO.md

@@ -3,5 +3,8 @@ Gaupol 0.92/1.0
 
 * [x] Fix error saving document from a time-based format to a
       frame-based or vice versa ([#28][])
+* [x] Fix error clicking undo or redo button dropdown arrow when no
+      document is yet open ([#29][])
 
 [#28]: https://github.com/otsaloma/gaupol/issues/28
+[#29]: https://github.com/otsaloma/gaupol/issues/29

gaupol/agents/menu.py

@@ -104,8 +104,13 @@ def _on_redo_button_show_menu(self, *args):
         for item in menu.get_children():
             menu.remove(item)
         self._redo_menu_items = []
-        page = self.get_current_page()
-        for i, action in enumerate(page.project.redoables):
+        redoables = []
+        with aeidon.util.silent(AttributeError):
+            # XXX: Gtk.Actionable.set_action_name doesn't affect the dropdown
+            # arrow making it clickable even when there's nothing to redo.
+            page = self.get_current_page()
+            redoables = page.project.redoables
+        for i, action in enumerate(redoables):
             item = Gtk.MenuItem(label=action.description)
             item.gaupol_index = i
             item.connect("activate", self._on_redo_menu_item_activate)
@@ -161,8 +166,13 @@ def _on_undo_button_show_menu(self, *args):
         for item in menu.get_children():
             menu.remove(item)
         self._undo_menu_items = []
-        page = self.get_current_page()
-        for i, action in enumerate(page.project.undoables):
+        undoables = []
+        with aeidon.util.silent(AttributeError):
+            # XXX: Gtk.Actionable.set_action_name doesn't affect the dropdown
+            # arrow making it clickable even when there's nothing to undo.
+            page = self.get_current_page()
+            undoables = page.project.undoables
+        for i, action in enumerate(undoables):
             item = Gtk.MenuItem(label=action.description)
             item.gaupol_index = i
             item.connect("activate", self._on_undo_menu_item_activate)