Bug: Error message when editing a built-in template

**Repro**
1) Click the New button to invoke the New Test Class dialog
2) Make sure one of the two default templates is selected
3) Click on the Modify the Selected Template button (third from the top on the right side of the list box)

**Observed**
"Invalid path or file name" error message is shown. The template is not opened.

**Expected**
To get a read-only copy of the embedded template