Only process cue-originated audio files if there is any.

(cherry picked from commit 4afaf5f058c682d7f2e1d7a9b51588dcd588b873)

src/NzbDrone.Core/MediaFiles/DiskScanService.cs

@@ -99,6 +99,8 @@ namespace NzbDrone.Core.MediaFiles
 
             var decisions = new List<ImportDecision<LocalTrack>>();
             var cueFiles = mediaFileList.Where(x => x.Extension.Equals(".cue")).ToList();
+            if (cueFiles.Count > 0)
+            {
                 mediaFileList.RemoveAll(l => cueFiles.Contains(l));
                 var cueSheetInfos = new List<CueSheetInfo>();
                 foreach (var cueFile in cueFiles)
@@ -134,6 +136,7 @@ namespace NzbDrone.Core.MediaFiles
                         mediaFileList.RemoveAll(x => cueSheetInfo.MusicFiles.Contains(x));
                     }
                 }
+            }
 
             decisions.AddRange(_importDecisionMaker.GetImportDecisions(mediaFileList, null, itemInfo, config));
 

src/NzbDrone.Core/MediaFiles/TrackImport/Manual/ManualImportService.cs

@@ -155,6 +155,8 @@ namespace NzbDrone.Core.MediaFiles.TrackImport.Manual
 
             // Split cue and non-cue files
             var cueFiles = audioFiles.Where(x => x.Extension.Equals(".cue")).ToList();
+            if (cueFiles.Count > 0)
+            {
                 audioFiles.RemoveAll(l => cueFiles.Contains(l));
                 var cueSheetInfos = new List<CueSheetInfo>();
                 foreach (var cueFile in cueFiles)
@@ -171,6 +173,7 @@ namespace NzbDrone.Core.MediaFiles.TrackImport.Manual
 
                     RemoveProcessedAudioFiles(audioFiles, cueSheetInfos, manualImportItems);
                 }
+            }
 
             var idOverrides = new IdentificationOverrides
             {
@@ -293,11 +296,15 @@ namespace NzbDrone.Core.MediaFiles.TrackImport.Manual
                     }
                 }
 
-                var singleFileReleaseDecisions = _importDecisionMaker.GetImportDecisions(audioFilesForCues, cueSheetInfos[0].IdOverrides, itemInfo, config, cueSheetInfos);
+                if (audioFilesForCues.Count > 0)
+                {
+                    var idOverrides = cueSheetInfos.Count > 0 ? cueSheetInfos[0].IdOverrides : null;
+                    var singleFileReleaseDecisions = _importDecisionMaker.GetImportDecisions(audioFilesForCues, idOverrides, itemInfo, config, cueSheetInfos);
                     var manualImportItems = UpdateItems(group, singleFileReleaseDecisions, replaceExistingFiles, disableReleaseSwitching);
                     result.AddRange(manualImportItems);
 
                     RemoveProcessedAudioFiles(audioFiles, cueSheetInfos, manualImportItems);
+                }
 
                 var idOverride = new IdentificationOverrides
                 {