sparse-checkout: free pattern list in sparse_checkout_list()

sparse-checkout: free pattern list in sparse_checkout_list()

In sparse_checkout_list(), we create a pattern_list that needs to
eventually be cleared. We remember to do so in the regular code path,
but the cone-mode path does an early return, and forgets to clean up.

We could fix the leak by adding a new call to clear_pattern_list(). But
we can simplify even further by just skipping the early return, pushing
the other code path (which consists now of only one line!) into an else
block. That also matches the same cone/non-cone if/else used in some
other functions.

This fixes 15 leaks found in t1091.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>