trivial: fix bloom filter init to isEmpty = true
trivial: fix bloom filter init to isEmpty = true

Fixes newly initialized bloom filters being
constructed with isEmpty(false), which still
works but loses the possible speedup when
checking for key membership in an empty filter.

dagurval/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt,bitcoinxt/bitcoinxt,bitcoinxt/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt,dagurval/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt