Fix restoration of cursor position and selection after undo/redo.

If a text selection was deleted, the selection should be restored by an
undo, but not if the selection was part of an atomic operation like
the DeleteStartOfWord key sequence.

Change-Id: Ia37f29c78f6367c60377c539c4e394e014485a49
Reviewed-by: Yann Bodson <yann.bodson@nokia.com>