Land rapid7#7392, stance check fix for HttpServer

Author: wvu

lib/msf/core/exploit/http/server.rb

@@ -73,7 +73,8 @@ def cli=(cli)
   end
 
   def print_prefix
-    if cli && !(stance == Msf::Exploit::Stance::Aggressive || stance.include?(Msf::Exploit::Stance::Aggressive))
+    if cli && self.respond_to?(:stance) &&
+        !(stance == Msf::Exploit::Stance::Aggressive || stance.include?(Msf::Exploit::Stance::Aggressive))
       super + "#{cli.peerhost.ljust(16)} #{self.shortname} - "
     else
       super