Fixed a bug in grn_select() which cause misinterpretation of drilldown_limit.
Fixed a bug in grn_select() which cause misinterpretation of drilldown_limit.

redfigure/groonga,hiroyuki-sato/groonga,redfigure/groonga,groonga/groonga,hiroyuki-sato/groonga,komainu8/groonga,naoa/groonga,naoa/groonga,groonga/groonga,hiroyuki-sato/groonga,naoa/groonga,komainu8/groonga,naoa/groonga,redfigure/groonga,hiroyuki-sato/groonga,naoa/groonga,kenhys/groonga,groonga/groonga,cosmo0920/groonga,cosmo0920/groonga,komainu8/groonga,naoa/groonga,komainu8/groonga,kenhys/groonga,redfigure/groonga,groonga/groonga,komainu8/groonga,naoa/groonga,myokoym/groonga,kenhys/groonga,cosmo0920/groonga,cosmo0920/groonga,groonga/groonga,kenhys/groonga,kenhys/groonga,kenhys/groonga,komainu8/groonga,hiroyuki-sato/groonga,redfigure/groonga,redfigure/groonga,redfigure/groonga,hiroyuki-sato/groonga,komainu8/groonga,cosmo0920/groonga,myokoym/groonga,komainu8/groonga,myokoym/groonga,cosmo0920/groonga,cosmo0920/groonga,groonga/groonga,myokoym/groonga,myokoym/groonga,cosmo0920/groonga,groonga/groonga,hiroyuki-sato/groonga,kenhys/groonga,groonga/groonga,hiroyuki-sato/groonga,redfigure/groonga,naoa/groonga,kenhys/groonga,myokoym/groonga,myokoym/groonga,myokoym/groonga