Previously, only an exact "0" was considered as no label.
This however, lead to inconsistent results when label ids were added manually to the query string.
Such as, "?labels=100,0" or "?labels=0,100".
closes#12649
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12665
Reviewed-by: Gusted <gusted@noreply.codeberg.org>