Chained token returning null

We ran into an issue where a chained token, in our case [node:og-group-ref:0:url:relative], was not returning a value.

I was able to trace its cause to the array of objects not being indexed in the same way as the token delta. So, for instance, the array of objects would be

array(8542 => )

instead of

array(0 => )

when using a delta of zero.

Patch attached to fix this issue.