Fixed: Fix NullRef in Subtitle Service due to #4924

(cherry picked from commit 89ee7d4452ae3b476e24aede89b668a3df2344fc)

src/NzbDrone.Core/Extras/Subtitles/SubtitleFile.cs

@@ -5,6 +5,11 @@ namespace NzbDrone.Core.Extras.Subtitles
 {
     public class SubtitleFile : ExtraFile
     {
+        public SubtitleFile()
+        {
+            LanguageTags = new List<string>();
+        }
+
         public Language Language { get; set; }
     }
 }