BUG - Import/Export dialog box lets you click OK when no extension are selected

[astrohart]

BUG: When zero items are selected in the list of check boxes of the ImportWindow, the OK button should be grayed out. The operation "clicking the OK button" is meaningless in this context and could lead to errors.

The acceptance criteria are as follows:
Given
I have selected either the Import Extensions or Export Extensions menu command and the ImportWindow is displayed
When
Zero entries in the check-box list of extensions are selected
Then
Clicking the OK button doesn't mean anything, so the OK button should be grayed out
Unless
More than zero entries in the Extensions list box are selected, in which case, the OK button should be enabled.

[astrohart]

I would ask that someone else please figure out how to fix this, as I am somewhat of a WPF newbie. 👍