Dispose get called twice.

[wakuflair]

Hi, I encoutered another problem with closing.

This also can be reproduced with Stylet.Samples.RedditBrowser sample, but need a bit of change:

1. Add IDisposable to the SubredditViewModel class.
2. Implement the Dispose method with any content.
3. Put a breakpoint inside the Dispose method.
4. Launch the sample application.
5. Open a tab, then click the Close button.
6. The breakpoint will be triggered twice.

[canton7]

Thanks for spotting this.

Technically this isn't an issue - the Microsoft guidelines are that Dispose methods may be called multiple times, and Dispose implementations should be resilient to this. That said, it's a bit ugly, so I'll try and fix.

[canton7]

I'll give it another day or two in case you spot something else, then push a new release.