Don't lose list position after installing KNS cursor themes

When installing a new cursor theme (or ditto uninstalling) from
KNewStuff, the current theme would become deselected due to a
full refresh of the theme list.

TEST PLAN
Install a theme using Get Hot New Stuff, see that after the list
refreshes, the current theme is reselected. Also uninstall a KNS
originated theme and see the same is true.

BUG:406084