Prevent an error when optional argument "overrides" is not passed

Prevent a potentially unexpected side-effect when the argument is passed.

nselib/smb.lua

@@ -133,6 +133,7 @@ local smbauth = require "smbauth"
 local stdnse = require "stdnse"
 local string = require "string"
 local table = require "table"
+local tableaux = require "tableaux"
 local unicode = require "unicode"
 local smb2 = require "smb2"
 _ENV = stdnse.module("smb", stdnse.seeall)
@@ -1093,6 +1094,8 @@ function list_dialects(host, overrides)
   local status, smb1_dialect
   local smbstate
 
+  overrides = tableaux.tcopy(overrides or {})
+
   -- Check for SMBv1 first
   stdnse.debug2("Checking if SMBv1 is supported")
   status, smbstate = start(host)

scripts/smb-protocols.nse

@@ -51,10 +51,9 @@ hostrule = function(host)
 end
 
 action = function(host,port)
-  local status, supported_dialects, overrides
+  local status, supported_dialects
   local output = stdnse.output_table()
-  overrides = {}
-  status, supported_dialects = smb.list_dialects(host, overrides)
+  status, supported_dialects = smb.list_dialects(host)
   if status then
     for i, v in pairs(supported_dialects) do -- Mark SMBv1 as insecure
       if v == "NT LM 0.12" then