[PATCH] Reject nonpositive Bloom filter element estimates

Hi, Hackers.

bloom_create() currently accepts a zero total_elems estimate. This
causes optimal_k() to divide by zero and then convert infinity to int,
which is undefined behavior.

The attached patch rejects nonpositive estimates before the calculation.
It also performs the bitset size multiplication as unsigned arithmetic
to avoid signed overflow for very large positive estimates, and adds a
regression test for the zero case.

The affected source and test module compile successfully, and
git diff --check passes.

Regards,
DaeMyung Kang