Segfault on malformed argument in setMulti()

Providing a malformed array as a parameter to setMulti() results in "Segmentation fault (core dumped)"

The issue can be replicated with the following script:
https://gist.github.com/8a08980573d47c22aecc#file-seg_fault-php

if instead of providing
$docs[]['TEST_DOC::' . $x] = '

';
we provide the correct structure
$docs['TEST_DOC::' . $x] = '

';

It works ok, but the first shouldn't segfault.