request: add missing OutOfMemory diag_set

In request_create_from_tuple and request_handle_sequence
we may be unable to request memory for tuples, don't
forget to setup diag error otherwise diag_raise will
lead to nil dereference.

Acked-by: Sergey Ostanevich <sergos@tarantool.org>
Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>