fix(core) Correctly detect LDAP error during login.

Avoids PHP errors and shows the actual LDAP error when there is a
 problem for fetching connected user.

issue #6175

include/class_ldap.inc

@@ -1119,7 +1119,7 @@ class LDAP
     if ($this->error == 'Success') {
       return 0;
     } else {
-      return ldap_errno($this->cid);
+      return @ldap_errno($this->cid);
     }
   }
 

include/class_userinfo.inc

@@ -87,6 +87,9 @@ class userinfo
     $ldap = $config->get_ldap_link();
     $ldap->cat($this->dn, ['*']);
     $attrs = $ldap->fetch(TRUE);
+    if (!$ldap->success()) {
+      throw new FusionDirectoryLdapError($this->dn, LDAP_SEARCH, $ldap->get_error(), $ldap->get_errno());
+    }
 
     $this->uid = $attrs['uid'][0];