#93 Find Flow crashing in Visio

[Ondřej Bouda]

The find flow algorithm is crashing in Visio, SCStudio version 0.5.3.

Steps to reproduce:
1. Open tests/membership/coregion_absolute.vsd
2. Issue the Find Flow dialog (SCStudio -> Find Flow)
3. Check "Page-1" in both flow and specification boxes and click Start
4. Visio crashes.