grn_obj_flush: lock only when WAL role is primary and WAL exists
grn_obj_flush: lock only when WAL role is primary and WAL exists

komainu8/groonga,komainu8/groonga,groonga/groonga,komainu8/groonga,groonga/groonga,groonga/groonga,groonga/groonga,komainu8/groonga,kenhys/groonga,komainu8/groonga,kenhys/groonga,groonga/groonga,kenhys/groonga,groonga/groonga,komainu8/groonga,kenhys/groonga,groonga/groonga,kenhys/groonga,komainu8/groonga,komainu8/groonga,kenhys/groonga,kenhys/groonga,kenhys/groonga,groonga/groonga