Inconsistent ways of getting object from ingest form after submitting file upload

Came across a minor inconsistency.

In most solution packs that offer a 'file upload' step, the submit handler for the file upload form includes the line [1]:

$object = $form_state['islandora']['objects'][0];

but disk image and web archive solution packs (and none other that I've found) use [2]:

$objects = &islandora_ingest_form_get_objects($form_state);
foreach ($objects as $object)

We should probably standardize to one or the other, unless there's a reason that disk image and web archive may be creating multiple objects simultaneously.

[1] https://github.com/Islandora/islandora_solution_pack_pdf/blob/d8bdb83f555c95be8cbfdeb43be4b4c57008b76d/includes/pdf_upload.form.inc#L74
[2] https://github.com/Islandora/islandora_solution_pack_disk_image/blob/53f61759939860b899b4d8ebdaf98ca4288329ba/includes/disk_image_upload.form.inc#L84 and https://github.com/Islandora/islandora_solution_pack_web_archive/blob/03cb35d6b7b3178d19ca2c8771760e02244774e2/includes/web_archive_upload.form.inc#L111