Fix lookup order of script args and allow plain 'name.arg' to be specified as 'arg'

nselib/stdnse.lua

@@ -832,20 +832,32 @@ end
 -- given. This works also for arguments given as top-level array values, like
 -- --script-args=unsafe; for these it returns the value 1.
 local function arg_value(argname)
+  -- First look for the literal script-arg name
+  -- as a key/value pair
   if nmap.registry.args[argname] then
     return nmap.registry.args[argname]
   end
-  -- if scriptname.arg is not there, check "arg"
-  local argument_frags = strsplit("%.", argname)
-  if nmap.registry.args[argument_frags[2]] then
-    return nmap.registry.args[argument_frags[2]]
-  end
-
+  -- and alone, as a boolean flag
   for _, v in ipairs(nmap.registry.args) do
     if v == argname then
       return 1
     end
   end
+
+  -- if scriptname.arg is not there, check "arg"
+  local shortname = argname:match("%.([^.]*)$")
+  if shortname then
+    -- as a key/value pair
+    if nmap.registry.args[shortname] then
+      return nmap.registry.args[shortname]
+    end
+    -- and alone, as a boolean flag
+    for _, v in ipairs(nmap.registry.args) do
+      if v == shortname then
+        return 1
+      end
+    end
+  end
   return nil
 end