* Fix hierarchical criteria performance issue
Don't apply recursive clause to hierarchical criteria when the depth is
set to 0 (i.e.: no recursion is needed).
This undoes the current performance penalty on for example the studios
page. This as reported in #1519, using a database of 4M images, 30K
scenes and 500 studios. Without this fix loading the studios overview,
with the default of 40 items per page, takes 6 to 7 seconds. With this
fix it only takes 0,07 seconds reverting the performance back to the
pre-hierarchical filtering performance (tested against 508f7b84 which
was the last commit before #1397 was merged).