file_data_sink_impl: Fix resource leak in close()
file_data_sink_impl: Fix resource leak in close()

close() should release resources even if it signals IO errors. Before
this patch _file would not be closed if wait() returned failed
future. Fix by closing in finally().

kjniemi/seastar,scylladb/seastar,cloudius-systems/seastar,dreamsxin/seastar,syuu1228/seastar,avikivity/seastar,cloudius-systems/seastar,scylladb/seastar,scylladb/seastar,avikivity/seastar,syuu1228/seastar,dreamsxin/seastar,syuu1228/seastar,kjniemi/seastar,cloudius-systems/seastar,avikivity/seastar,dreamsxin/seastar,kjniemi/seastar