check if constant aliases are already set before setting

(I'm presuming that was what removing was intended to help with)

Author: Brent Cook

lib/msf/core/exploit/ntlm.rb

@@ -5,11 +5,11 @@
 require 'rex/proto/ntlm/message'
 require 'rex/proto/ntlm/utils'
 
-NTLM_CONST   = ::Rex::Proto::NTLM::Constants
-NTLM_CRYPT   = ::Rex::Proto::NTLM::Crypt
-NTLM_UTILS   = ::Rex::Proto::NTLM::Utils
-NTLM_BASE    = ::Rex::Proto::NTLM::Base
-NTLM_MESSAGE = ::Rex::Proto::NTLM::Message
+NTLM_CONST   ||= ::Rex::Proto::NTLM::Constants
+NTLM_CRYPT   ||= ::Rex::Proto::NTLM::Crypt
+NTLM_UTILS   ||= ::Rex::Proto::NTLM::Utils
+NTLM_BASE    ||= ::Rex::Proto::NTLM::Base
+NTLM_MESSAGE ||= ::Rex::Proto::NTLM::Message
 
 module Msf