Fix which method in functions.prf on Windows.

The first "set _endwhich" needs a value to work well.

Change-Id: I1fb65b71dd7dd378de62d2836ba003d54787cd23
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>