Fix a bug that needed bulk buffer isn't allocated automatically
Fix a bug that needed bulk buffer isn't allocated automatically

It is caused only for weight uvector (vector of grn_id) bulk.

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