Pixelate/blur fields are not updated when image effects are applied

[bitboy85]

Describe the bug
Pixelate fields are not updated when image effects are applied

To Reproduce
Steps to reproduce the behavior:

1. Take a screenshot
2. Add a pixelate or blur field
3. Use an image effect like "invert colors" or "grey scale"
4. Result: The pixelate or blur fields showing "the old colors"

Expected behavior
Pixelate/blur fields should automatically update.

Workaround
Move the pixelate/blur field

Desktop (please complete the following information):

• OS: Linuxmint
• ksnip version 1.9.0