fakevim: Fix crash when adding text to last line

Workaround for crash when in edit block and adding text to the last
empty line.

Change-Id: I46b84074bd6f6fbcae698671716e151ebab98f5b
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: hjk <qthjk@ovi.com>