This commit reverts a previous optimization attempt 3f588cd4a that
tried to trim or shrink the array of child searchers in a
search-disjunction.
Although I am not sure why at the moment, that optimization
incorrectly broke higher level boolean queries, but reverting so that
functionality is restored.
Disjunction searchers are used heavily by higher-level searchers, like
prefix searchers. In that case, a disjunction searcher might have
many thousands of child searchers.
This commit adds an optimization to close each child term searcher as
soon as a child searcher is finished and remove it from the
disjunction searcher's children.