UI: Only show DLC RomFS button under Extract Data when DLCs are available.

Also convert the constructor of DlcSelectViewModel to expect a normal title id and not one already converted to the base ID.

src/Ryujinx/UI/ViewModels/DlcSelectViewModel.cs

@@ -34,9 +34,7 @@ namespace Ryujinx.Ava.UI.ViewModels
         
         public DlcSelectViewModel(ulong titleId, ApplicationLibrary appLibrary)
         {
-            _dlcs = appLibrary.DownloadableContents.Items
-                .Where(x => x.Dlc.TitleIdBase == titleId)
-                .Select(x => x.Dlc)
+            _dlcs = appLibrary.FindDlcsFor(titleId)
                 .OrderBy(it => it.IsBundled ? 0 : 1)
                 .ThenBy(it => it.TitleId)
                 .ToArray();

src/Ryujinx/UI/ViewModels/MainWindowViewModel.cs

@@ -481,6 +481,8 @@ namespace Ryujinx.Ava.UI.ViewModels
             }
         }
 
+        public bool HasDlc => ApplicationLibrary.HasDlcs(SelectedApplication.Id);
+
         public string CacheLoadStatus
         {
             get => _cacheLoadStatus;