media_get_file_without_label() WSOD with Drupal 7 RC1

Looks like $format['settings'] can be NULL in media_get_file_without_label() in which case, the array_merge() will result in NULL instead of array() and then the subsequent call to field_field_view() ends up with a WSOD in _field_info_prepare_instance_display() where the += array operator is being used on a NULL derived from this settings array.

This patch certainly fixes the issue, ensuring arrays are used for array_merge(). Maybe it can be tracked down to a field_info_instance() bug, not sure its settings value is intended to be used right away this way.