Unset current row of event list before clearing it.

Closes PacktPublishing#16.

Thanks eramey16!

Author: alandmoore

Chapter03/calendar_app.py

@@ -146,6 +146,11 @@ def clear_form(self):
         self.event_detail.setPlainText('')
 
     def populate_list(self):
+        # As reported by github user eramey16, we need the following line
+        # to unselect list items since the selected index may not exist
+        # in the new list.  This line is not in the book code.
+        self.event_list.setCurrentRow(-1)
+
         self.event_list.clear()
         self.clear_form()
         date = self.calendar.selectedDate()