MT#62568 fix get_subscriber_enable_2fa() and get_chained_preference_rs()

* get_chained_preference_rs() now returns undef if the provided
  preference does not exist
* fix Utils::Auth::get_subscriber_enable_2fa() also check if
  $rs is defined, in case if 'enable_2fa' preference does not
  exists in the database.

Change-Id: Iffd7abc39c4e62a0c81a74a4dc18c04477445d34

lib/NGCP/Panel/Utils/Auth.pm

@@ -878,7 +878,7 @@ sub get_subscriber_enable_2fa {
         },
     );
 
-    if ($rs->first) {
+    if ($rs && $rs->first) {
         return 1 if $rs->first->value;
     }
 

lib/NGCP/Panel/Utils/Preferences.pm

@@ -2529,6 +2529,8 @@ sub get_chained_preference_rs {
         ->resultset('voip_preferences')
         ->find({ attribute => $attr });
 
+    return unless $preference;
+
     my $type_meta = $params->{type} // 'usr';
     my $type_order = $params->{order} // $type_order_default->{$type_meta};
     my $provisioning_subscriber = $params->{provisioning_subscriber};