Empty error on zero rows input

[DifferentialOrange]

./doc/playground.lua

tarantool> crud.insert_object_many('customers', {})
---
- null
- []
...

If an empty array is passed as argument, result is nil, errs, yet errs is an empty array.

The case may seem synthetic at the first glance, but it is rather easy to get into such situation while calling CRUD from go-tarantool and spend a couple of hours trying to explore what went wrong when error is non-nil, yet empty.