In category input field, typing invalid category name doesn't clear suggestions.

To reproduce:

1. Open page options dialog, "Categories" tab.
2. Type a potentially valid category name, such as "A". Wait for suggestions to appear.
3. Type in something invalid, such as "<", afterwards.
   • From this point on, as long as the category name stays invalid, the suggestions will not be updated, even if the original "A" is deleted and replaced with, say, "Z".
   • De-focusing the field and re-focusing it will clear suggestions.
   • Deleting invalid characters will display correct suggestions again.