Fix ItemByTitleHelper site/title combinations.

Fixes ItemByTitleHelper by allowing back requests with one title
and multiple sites, which had been forbidden in Ib04b5dd5. Requests
can now accept one title and multiple sites, one site and multiple
titles, or an equal number of sites and titles.

Bug: 59676
Change-Id: I34ae872ec2795ad4b3e064c78bbe5596e0dcfdd5