Fix suppressed relay of query to in-memory indexer.
Fix suppressed relay of query to in-memory indexer.

Because loading a bitmap indexer performed a check of the corresponding path on
disk, a partition would report non-existant indexers if they haven't been
flushed. With this fix, a partition now relays the query predicate to
not-yet-flushed indexers.

Relates #59.

vast-io/vast,vast-io/vast,mavam/vast,mavam/vast,mavam/vast,pmos69/vast,vast-io/vast,vast-io/vast,vast-io/vast,pmos69/vast,mavam/vast,pmos69/vast,pmos69/vast