_queueFindEnrichment allows two thumbnail starts per frame, but it counted a
row against that allowance even when _startFindThumb ignored it. A row already
resolved to "failed", or with no thumbnail at all, is ignored there, so two such
rows above a card spent the allowance every frame and the card never got a
download. It stayed on its MOD placeholder (no spinner) for the whole session.
Skip rows that have already resolved, so only a row that actually starts a
download is counted. Adds a regression test that fails without the change.
Code-Grub