Revising segmentations: erase button works only if paint button ahs been done

[maxradx]

Describe the bug
When revising segmentations (e.g. from automated models), if the annotators wants to erase some masks using load latest masks, then the user currently must do paint before using erase. this is inconvenient since some times only some erasing should be done

To Reproduce
Steps to reproduce the behavior:

1. Open slicer, new configuration, select volumes and output folders
2. Load latest masks
3. Erase from the SlicerCART UI
4. see that nothing is done (but if you click on paint before, then it will work)

Expected behavior
Be able to paint or erase no matter previous action