grn_window_execute: don't run window function if all tables are context table
grn_window_execute: don't run window function if all tables are context table

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