Fixed: Ensure indexer errors are handled before processing response

(cherry picked from commit 76f93c8415419f0c3dab90582d47a1c9a653263c)

Closes #2458

src/NzbDrone.Core/Indexers/Torznab/TorznabRssParser.cs

@@ -19,6 +19,11 @@ namespace NzbDrone.Core.Indexers.Torznab
 
         protected override bool PreProcess(IndexerResponse indexerResponse)
         {
+            if (indexerResponse.HttpResponse.HasHttpError)
+            {
+                base.PreProcess(indexerResponse);
+            }
+
             var xdoc = LoadXmlDocument(indexerResponse);
             var error = xdoc.Descendants("error").FirstOrDefault();