[BUG - experimental branch] NOR when trying to access invalid super field

[NotHyper-474]

With the changes of 0337d2e to PolymodInterpEx, attempts to access a non-existent field on a superclass aren't properly handled anymore; because all script# functions assume the ASC isn't null this causes a Null Object Reference error.

Expected Behavior

I should get an Invalid Field Access error instead.

[NotHyper-474]

For the record, doing this will now correctly yield an invalid field access error, but for functions it will incorrectly display __super_fieldName for the field name.