Fix crash when Colorize Tool is active on closing Krita

Steps to reproduce:

1. Create a layer with colorize mask
2. Disable "Show key strokes" on the mask (important)
3. Select "Colorize Tool"
4. Click on the mask, to lazily activate key strokes
5. Close Krita -> Crash

The crash happened because of some weird update signals coming
after KisView was actually destroyed.