Console exception when pressing cancel on the test discovery fail dialog

[freakboy3742]

Issue #5 reported a problem with the test discovery error dialog: if you had a problem with your test suite, you would get stuck in a continuous loop of dialogs being shown with no way to exit.

The solution for that bug was to add a cancel button to escape the loop. However, if you get the dialog on first startup and hit cancel, an exception is raised at the shell prompt. This isn't inherently a problem, but it is a bit messy.