Fix render factory handling of multiple items

Problem/Motivation

The RendererFactory class has a comment documenting how multiple items (in an array) should be handled:

// If we get an array or something, just look at the first one.

However, the code is looking at the last item instead of the first:

    if (is_array($item)) {
      $item = array_pop($item);
    }

Proposed resolution

Use the php reset array function instead of array_pop.