fix incorrect BooleanSearcher Advance behavior
fix incorrect BooleanSearcher Advance behavior

* Revert "Advancing boolean searcher's currentID w.r.t currMustNot"

This reverts commit dd49ef0aa0a006a46e90b20dcba578265c043c07.

* track boolean searcher done status

when boolean searchers are nested, there can occur a situation
in which a boolean searcher is reset after reaching the end.

this leads to incorrect behavior, so instead we track reaching
the end, and prevent advance from resetting that behavior.

* add Unit test that catches a cornercase:
    TestNestedBooleanMustNotSearcherUpsidedown

blevesearch/bleve,blevesearch/bleve