[FIX] Bug 267: wsdl fails with "Argument is out of range."

This fix bug 267
https://bugzilla.xamarin.com/show_bug.cgi?id=267

in mcs/class/System.Web.Services
make run-test PROFILE=net_2_0 ok
make run-test PROFILE=net_4_0 ok
make run-test PROFILE=net_4_5 ok