The scorerNodeQueue contains all subscorers ordered by their current
docID(), with the minimum at the top.
The scorerNodeQueue is initialized the first time nextDoc() or advance() is
called.
An exhausted scorer is immediately removed from the scorerDocQueue.
If less than the minimumNrMatchers scorers remain in the scorerDocQueue
nextDoc() and advance() return false.
After each to call to nextDoc() or advance() currentScore
is
the total score of the current matching doc, nrMatchers
is the
number of matching scorers, and all scorers are after the matching doc, or
are exhausted.