fix saving smart collection (#1384)

ErsatzTV/Shared/SaveAsSmartCollectionDialog.razor

@@ -45,7 +45,7 @@
     private readonly SmartCollectionViewModel _newCollection = new(-1, "(New Collection)", string.Empty);
     private string _newCollectionName;
 
-    private List<SmartCollectionViewModel> _collections;
+    private List<SmartCollectionViewModel> _collections = new();
 
     private SmartCollectionViewModel _selectedCollection;