0.98.2: Filter is retained by mistake

[Mapaler]

XnView: MP 0.98.2 - 64-bit
OS: Windows 10 - 64-bit

Effect: The filter is incorrectly retained in the picture result and is not undone.

To reproduce:

• Open a picture and select the Filter
  图像 27.png
• Checked the Apply to image
• Select a Filter that can see the changes
• Then click several times Undo
• The filter is loaded on the image
  图像 29.png
• Click Cancel
• The picture will retain all the Filter change
  And switching with the front or back pictures is still preserved
  图像 30.png
  However, the real file has not been modified