field_group_pack sometimes called on already-packed groups

field_group_pack can be called on a group that already has its properties under a 'data' superproperty; this kills the group. This happens if you call ctools_export_crud_load and then later save its output with ctools_export_crud_save. There should be a check in field_group_pack to make sure it's not blowing away data.

Patch forthcoming when I have an issue number.