Preserving numeric keys on #each helper, to maintain @key data variable functioning on int arrays

Assuming an array should be printed out like (enableDataVariables set to true):

{{#each arr}}
    {{ @key }}:   {{ this }}
{{/each}}

which was defined as

$arr = [
    '19' => 5
];

(key can be any integer)
The resulting @key variable was always printed as 0. array_slicein the helper function caused numeric keys to be set to 0 while maintaing string keys correctly. The pull request is enabling explicit key preserving, to fix such issue.