History check shouldn't die if download client is not configured.

Do not log exceptron response when no errors are found

src/NzbDrone.Core/DecisionEngine/Specifications/RssSync/HistorySpecification.cs

@@ -41,7 +41,9 @@ namespace NzbDrone.Core.DecisionEngine.Specifications.RssSync
                 return true;
             }
 
-            if (_downloadClientProvider.GetDownloadClient().GetType() == typeof (Sabnzbd))
+            var downloadClient = _downloadClientProvider.GetDownloadClient();
+
+            if (downloadClient != null && downloadClient.GetType() == typeof (Sabnzbd))
             {
                 _logger.Trace("Performing history status check on report");
                 foreach (var episode in subject.Episodes)

src/NzbDrone.Host/Owin/NlogTextWriter.cs

@@ -32,7 +32,7 @@ namespace NzbDrone.Host.Owin
 
         public override void Write(string value)
         {
-            if (value.ToLower().Contains("error") && !value.ToLower().Contains("sqlite"))
+            if (value.ToLower().Contains("error") && !(value.ToLower().Contains("sqlite") || value.ToLower().Contains("\"errors\":null")))
             {
                 _logger.Error(value);
             }