Position lost after canceled edits

[Nick Vallianos]

Torsten: This happens when you add a new node (via Alt-A or the "Add" button) and then
press Escape to cancel the edit of the newly added empty node. After this, no
node is selected and the keyboard focus seems to be on the first node. I think
it would make sense to restore the focus to the state before the canceled
addition of a new node.

[Nick Vallianos (nval)]

1681:
Odot::CellRendererText is the task editing widget. One instance is always
around, getting text of tasks to be edited or starting new empty ones. When
it is called in to edit a task, it gets its path and goes there. When a new
blank task is initiated, its path is also created. When the editing is
done, the task editor disappears and the focus goes to that same path,
This is the desired behaviour when a task has been created, but if the
editing has been escaped, no task is created and that path leads to nowhere.
This leads to the focus going to the root of the tree.

One solution would be to always store the previous path when a new item is
being created, and restore it once escape has been pressed.

Another solution would be to move to a default, e.g. the parent, but this
may be wrong, for example when a sibling has been created.