After removing a category, editing category sortkeys no longer works.

Steps to reproduce:

1. Edit a page using VisualEditor
2. Open Options → Categories dialog
3. Click a category, then the trashcan to remove it (if there are no categories, add one first, then remove it)
4. Click another category, then try to change its sort key (if there are no categories, add one first)

Expected: after closing the popup, the sort key is saved. Actual: after closing the popup, the sort key is lost.