MDL-42723: Hide and handle LDAP error when user not in context being …

…checked

MDL-41304 only fixed the case when 'Search subcontext' is enabled. We need to
fix the case when it's not enabled too.

While silencing errors with an @ should be avoided if possible, there's no
other way to prevent the warnings in this case.

lib/ldaplib.php

@@ -247,15 +247,17 @@ function ldap_find_userdn($ldapconnection, $username, $contexts, $objectclass, $
         }
 
         if ($search_sub) {
-            if (!$ldap_result = @ldap_search($ldapconnection, $context,
-                                           '(&'.$objectclass.'('.$search_attrib.'='.ldap_filter_addslashes($username).'))',
-                                           array($search_attrib))) {
-                break; // Not found in this context.
-            }
+            $ldap_result = @ldap_search($ldapconnection, $context,
+                                        '(&'.$objectclass.'('.$search_attrib.'='.ldap_filter_addslashes($username).'))',
+                                        array($search_attrib));
         } else {
-            $ldap_result = ldap_list($ldapconnection, $context,
-                                     '(&'.$objectclass.'('.$search_attrib.'='.ldap_filter_addslashes($username).'))',
-                                     array($search_attrib));
+            $ldap_result = @ldap_list($ldapconnection, $context,
+                                      '(&'.$objectclass.'('.$search_attrib.'='.ldap_filter_addslashes($username).'))',
+                                      array($search_attrib));
+        }
+
+        if (!$ldap_result) {
+            continue; // Not found in this context.
         }
 
         $entry = ldap_first_entry($ldapconnection, $ldap_result);