Fix: Fixed NullReferenceException in BaseDeleteAction.DeleteItemsAsync (#15467)

Co-authored-by: 0x5BFA <62196528+0x5bfa@users.noreply.github.com>

Author: hishitetsu

src/Files.App/Actions/FileSystem/BaseDeleteAction.cs

@@ -34,9 +34,11 @@ item.PrimaryItemAttribute is StorageItemTypes.File
 							? FilesystemItemType.File
 							: FilesystemItemType.Directory));
 
-			await context.ShellPage!.FilesystemHelpers.DeleteItemsAsync(items, settings.DeleteConfirmationPolicy, permanently, true);
-
-			await context.ShellPage.FilesystemViewModel.ApplyFilesAndFoldersChangesAsync();
+			if (context.ShellPage is IShellPage shellPage)
+			{
+				await shellPage.FilesystemHelpers.DeleteItemsAsync(items, settings.DeleteConfirmationPolicy, permanently, true);
+				await shellPage.FilesystemViewModel.ApplyFilesAndFoldersChangesAsync();
+			}
 		}
 
 		private void Context_PropertyChanged(object? sender, PropertyChangedEventArgs e)