Fix a bug for backwards compatibility

Author: agix

lib/msf/core/exploit/smb/psexec.rb

@@ -52,7 +52,7 @@ def smb_read_file(smbshare, host, file)
   # @param command [String] Should be a valid windows command
   # @param disconnect [Boolean] Disconnect afterwards
   # @return [Boolean] Whether everything went well
-  def psexec(command, service_description,disconnect=true)
+  def psexec(command, disconnect=true, service_description=nil)
     simple.connect("\\\\#{datastore['RHOST']}\\IPC$")
     handle = dcerpc_handle('367abb81-9844-35f1-ad32-98f038001003', '2.0', 'ncacn_np', ["\\svcctl"])
     vprint_status("#{peer} - Binding to #{handle} ...")