Fix for RegionDialogService

[ComtelJeremy]

Brian,

Thank you for your good work with Prism and your videos. I have been watching the PrismOutlook series, and learning a lot as I am beginning to understand your approach to problems, which helps me understand Prism and how to use it as designed.

For fun and education (and perhaps in a future project, profit) I have tried to make the RegionDialogService work.
It actually took very little change from what you had on the video before you abandoned it. Scoping seemed to be the major issue.

I know you are a very busy person, so feel free to ignore and close this (or ask me to), but I thought I would let you know in case it is of any use or curiosity to you. I have forked the repo, and made the changes in a branch in the fork:
Commit in my fork

I would love your comments, but again, I know how precious time is.

Regards, and thank you again for your work with Prism.

Jeremy