kfwlogon corrections for XP

kfwlogon corrections for XP

This patch addresses a problem discovered on some XP systems.
After rundll32.exe starts, the CreateProcess can fail to
start kfwcpcc.exe if the current directory is not %WinDir%\System32.
CreateProcess() should be called with the lpApplicationName parameter
set to NULL in order to permit the use of the PATH.

Also, in ConfigureLogonScript ensure that the trailing NUL of the
constructed command line is processed when producing the wide
character version of the string.

ticket: new
component: windows
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@19488 dc483132-0cff-0310-8789-dd5450dbe970