IndexedAutocomplete: negated rating metatags get completed to non-negated

[NamelessContributor]

Typing -rating:s<tab> results in rating:safe. The other metatags I tested aren't affected.
Tested on both Firefox and Chrome.

[BrokenEagle]

This issue was actually affecting all of the static metatags, i.e. parent, child, status, etc. The script was upgraded to Version 28.28 with a70222f which should fix this issue.