Improve default path for Synology Download Station

Fixes: Missing default path for Download Station
Fixes: Error when getting destination path for Synology Download Station in health check

(cherry picked from commit 4bf3ab1511b4ea25642476bf9df13f91b6f73d76)

src/NzbDrone.Core.Test/Download/DownloadClientTests/DownloadStationTests/TorrentDownloadStationFixture.cs

@@ -431,7 +431,7 @@ namespace NzbDrone.Core.Test.Download.DownloadClientTests.DownloadStationTests
             id.Should().NotBeNullOrEmpty();
 
             Mocker.GetMock<IDownloadStationTaskProxy>()
-                  .Verify(v => v.AddTaskFromUrl(It.IsAny<string>(), null, It.IsAny<DownloadStationSettings>()), Times.Once());
+                  .Verify(v => v.AddTaskFromUrl(It.IsAny<string>(), _defaultDestination, It.IsAny<DownloadStationSettings>()), Times.Once());
         }
 
         [Test]

src/NzbDrone.Core.Test/Download/DownloadClientTests/DownloadStationTests/UsenetDownloadStationFixture.cs

@@ -308,7 +308,7 @@ namespace NzbDrone.Core.Test.Download.DownloadClientTests.DownloadStationTests
             id.Should().NotBeNullOrEmpty();
 
             Mocker.GetMock<IDownloadStationTaskProxy>()
-                  .Verify(v => v.AddTaskFromData(It.IsAny<byte[]>(), It.IsAny<string>(), null, It.IsAny<DownloadStationSettings>()), Times.Once());
+                  .Verify(v => v.AddTaskFromData(It.IsAny<byte[]>(), It.IsAny<string>(), _defaultDestination, It.IsAny<DownloadStationSettings>()), Times.Once());
         }
 
         [Test]

src/NzbDrone.Core/Download/Clients/DownloadStation/TorrentDownloadStation.cs

@@ -450,14 +450,15 @@ namespace NzbDrone.Core.Download.Clients.DownloadStation
             {
                 return Settings.TvDirectory.TrimStart('/');
             }
-            else if (Settings.MusicCategory.IsNotNullOrWhiteSpace())
-            {
+
             var destDir = GetDefaultDir();
 
+            if (Settings.MusicCategory.IsNotNullOrWhiteSpace())
+            {
                 return $"{destDir.TrimEnd('/')}/{Settings.MusicCategory}";
             }
 
-            return null;
+            return destDir.TrimEnd('/');
         }
     }
 }

src/NzbDrone.Core/Download/Clients/DownloadStation/UsenetDownloadStation.cs

@@ -426,14 +426,15 @@ namespace NzbDrone.Core.Download.Clients.DownloadStation
             {
                 return Settings.TvDirectory.TrimStart('/');
             }
-            else if (Settings.MusicCategory.IsNotNullOrWhiteSpace())
-            {
+
             var destDir = GetDefaultDir();
 
+            if (Settings.MusicCategory.IsNotNullOrWhiteSpace())
+            {
                 return $"{destDir.TrimEnd('/')}/{Settings.MusicCategory}";
             }
 
-            return null;
+            return destDir.TrimEnd('/');
         }
     }
 }