Fixed mask framebuffer not unlocked

src/PixiEditor.AvaloniaUI/Models/DocumentModels/ActionAccumulator.cs

@@ -160,7 +160,7 @@ internal class ActionAccumulator
         foreach (var child in root.Children)
         {
             lockedFramebuffers.Add(child.PreviewBitmap?.Lock());
-            child.MaskPreviewBitmap?.Lock();
+            lockedFramebuffers.Add(child.MaskPreviewBitmap?.Lock());
             if (child is IFolderHandler innerFolder)
                 LockPreviewBitmaps(innerFolder, lockedFramebuffers);
         }

src/PixiEditor.AvaloniaUI/ViewModels/Document/StructureMemberViewModel.cs

@@ -152,7 +152,13 @@ internal abstract class StructureMemberViewModel : ObservableObject, IStructureM
     }
     public DrawingSurface? PreviewSurface { get; set; }
 
-    public WriteableBitmap? MaskPreviewBitmap { get; set; }
+    private WriteableBitmap? maskPreviewBitmap;
+
+    public WriteableBitmap? MaskPreviewBitmap
+    {
+        get => maskPreviewBitmap;
+        set => SetProperty(ref maskPreviewBitmap, value);
+    }
 
     public DrawingSurface? MaskPreviewSurface { get; set; }