Port reduction crash fix

fix for issue :
When CBN code changes and cause less number of ports like in picture,
![cbnporterror](https://f.cloud.github.com/assets/5274938/1471055/e661f02e-45d2-11e3-9f90-a9aa491fca22.JPG)

Then any connector attached to the port being deleted will redraw itself, and will crash when it cannot find the port model. 

 Tried to simulate this in a test by opening a file and changing the code directly. Didnt work :| Not sure how to test this.