Dedupe releases based on indexer priority

(cherry picked from commit 38c717bcef6fa5fcd2ff1c7901639eb888a94a8a)

Closes #2727

src/NzbDrone.Core/IndexerSearch/ReleaseSearchService.cs

@@ -165,8 +165,10 @@ namespace NzbDrone.Core.IndexerSearch
 
         private List<DownloadDecision> DeDupeDecisions(List<DownloadDecision> decisions)
         {
-            // De-dupe reports by guid so duplicate results aren't returned. Pick the one with the least rejections.
-            return decisions.GroupBy(d => d.RemoteBook.Release.Guid).Select(d => d.OrderBy(v => v.Rejections.Count()).First()).ToList();
+            // De-dupe reports by guid so duplicate results aren't returned. Pick the one with the least rejections and higher indexer priority.
+            return decisions.GroupBy(d => d.RemoteBook.Release.Guid)
+                .Select(d => d.OrderBy(v => v.Rejections.Count()).ThenBy(v => v.RemoteBook?.Release?.IndexerPriority ?? IndexerDefinition.DefaultPriority).First())
+                .ToList();
         }
     }
 }

src/NzbDrone.Core/Indexers/IndexerDefinition.cs

@@ -4,6 +4,13 @@ namespace NzbDrone.Core.Indexers
 {
     public class IndexerDefinition : ProviderDefinition
     {
+        public const int DefaultPriority = 25;
+
+        public IndexerDefinition()
+        {
+            Priority = DefaultPriority;
+        }
+
         public bool EnableRss { get; set; }
         public bool EnableAutomaticSearch { get; set; }
         public bool EnableInteractiveSearch { get; set; }
@@ -11,7 +18,7 @@ namespace NzbDrone.Core.Indexers
         public DownloadProtocol Protocol { get; set; }
         public bool SupportsRss { get; set; }
         public bool SupportsSearch { get; set; }
-        public int Priority { get; set; } = 25;
+        public int Priority { get; set; }
 
         public override bool Enable => EnableRss || EnableAutomaticSearch || EnableInteractiveSearch;