Hang when expected number of items is zero

When the expected number of items is zero, the number of hashes becomes u32::MAX. To see the behavior, try this program: ```rust use fastbloom::BloomFilter; fn main() { for expected in std::iter::once(0).chain((0..10).map(|exponent| 1 << exponent)) { let bloom_filter = BloomFilter::with_false_pos(0.001).expected_items(expected); println!( "expected={expected} num_hashes={}", bloom_filter.num_hashes() ); } } ``` The output with fastbloom 0.14.0: ``` expected=0 num_hashes=4294967295 expected=1 num_hashes=354 expected=2 num_hashes=177 expected=4 num_hashes=88 expected=8 num_hashes=44 expected=16 num_hashes=22 expected=32 num_hashes=11 expected=64 num_hashes=10 expected=128 num_hashes=10 expected=256 num_hashes=10 expected=512 num_hashes=10 ``` Computing u32::MAX hashes effectively hangs the program. The number of hashes for small numbers of expected items also seems very large (354 for 1 item?), but doesn't hang the program at least.