Always do MaxCardinality checks.

Stockfish currently relies on the "filter_root_moves" function also
having the side effect of clamping Cardinality against MaxCardinality
(the actual piece count in the tablebases). So if we skip this function,
we will end up probing in the search even without tablebases installed.

We cannot bail out of this function before this check is done, so move
the MultiPV hack a few lines below.