RtlGetDaclSecurityDescriptor crash on NULL pointer

[Bobby Bingham]

Installing winamp5 with winver=winxp reveals that the wma installer
calls GetSecurityDescriptorDacl with pSecurityDescriptor == NULL, which
then calls RtlGetDaclSecurityDescriptor, which immediately dereferences
it and crashes.

Reading MSDN indicates that pSecurityDescriptor may be NULL, but I don't
know the first thing about NT security descriptors, and so I'm not sure
what the right way to handle it is.  But I thought I'd at least point it
out so someone who does know could take a look.

--
Bobby Bingham