merger: non-array tuple in a buffer leads to assertion fail

Tarantool version: 2.5.0-62-gbb7c3d167 (in fact since merger was introduced in 2.2.0-268-gc7915eccd).

#!/usr/bin/env tarantool

local buffer = require('buffer')
local msgpack = require('msgpack')
local merger = require('merger')

local tuple = 1 -- Not an array!
local buf = buffer.ibuf()
msgpack.encode({tuple}, buf)

local exp_err = 'A tuple must be an array'
local source = merger.new_source_frombuffer(buf)
local ok, err = pcall(source.select, source)
assert(ok == true, ':select() should fail')
assert(err == exp_err, 'verify error message')

os.exit(0)

Expected result: zero exit code.

Actual result:

$ ./case.lua 
tarantool: /var/tmp/portage/dev-db/tarantool-9999/work/tarantool-9999/src/box/tuple.h:894: mp_tuple_assert: Assertion `mp_typeof(*tuple) == MP_ARRAY' failed.
Aborted