MDL-9399 auth/ldap: NTLM SSO - move textlib conversion earlier

From Iñaki Arenaza - fix for

... I forgot to put the textlib conversion
call before the block of code that uses $extusername, so it
completely breaks the user validation process.

auth/ldap/auth.php

@@ -85,6 +85,10 @@ function user_login($username, $password) {
             return false;
         }
 
+        $textlib = textlib_get_instance();
+        $extusername = $textlib->convert(stripslashes($username), 'utf-8', $this->config->ldapencoding);
+        $extpassword = $textlib->convert(stripslashes($password), 'utf-8', $this->config->ldapencoding);
+
         //
         // Before we connect to LDAP, check if this is an AD SSO login
         // if we succeed in this block, we'll return success early.
@@ -125,10 +129,6 @@ function user_login($username, $password) {
         unset($key);
 
 
-        $textlib = textlib_get_instance();
-        $extusername = $textlib->convert(stripslashes($username), 'utf-8', $this->config->ldapencoding);
-        $extpassword = $textlib->convert(stripslashes($password), 'utf-8', $this->config->ldapencoding);
-
         $ldapconnection = $this->ldap_connect();
 
         if ($ldapconnection) {