Fixed: (Avistaz) Empty query failing with error

Fixes #192

src/NzbDrone.Core/Indexers/Definitions/Avistaz/AvistazParser.cs

@@ -24,6 +24,11 @@ namespace NzbDrone.Core.Indexers.Definitions.Avistaz
         {
             var torrentInfos = new List<TorrentInfo>();
 
+            if (indexerResponse.HttpResponse.StatusCode == HttpStatusCode.NotFound)
+            {
+                return torrentInfos.ToArray();
+            }
+
             if (indexerResponse.HttpResponse.StatusCode != HttpStatusCode.OK)
             {
                 throw new IndexerException(indexerResponse, $"Unexpected response status {indexerResponse.HttpResponse.StatusCode} code from API request");

src/NzbDrone.Core/Indexers/HttpIndexerBase.cs

@@ -441,7 +441,7 @@ namespace NzbDrone.Core.Indexers
                 response = await _httpClient.ExecuteAsync(request.HttpRequest);
             }
 
-            // Throw any other http error we get after attempting auth
+            // Throw common http errors here before we try to parse
             if (response.HasHttpError)
             {
                 _logger.Warn("HTTP Error - {0}", response);
@@ -450,10 +450,6 @@ namespace NzbDrone.Core.Indexers
                 {
                     throw new TooManyRequestsException(request.HttpRequest, response);
                 }
-                else
-                {
-                    throw new HttpException(request.HttpRequest, response);
-                }
             }
 
             UpdateCookies(Cookies, DateTime.Now + TimeSpan.FromDays(30));