Bug 9993: On editing basket group delivery place resets to logged in branch

Bug 9993: On editing basket group delivery place resets to logged in branch

This patch modifies basketgroups.pl so that existing data about a basket
group's billing and delivery place are correctly preselected in the edit
form. These fields shouldn't reset to the logged-in user's home branch
just because they have an empty value.

To test, apply the patch and go to Acquisitions -> Vendor -> Basket
groups.

When adding or editing a basket group the pre-selected value for
"Billing place" and "Delivery place" should be correct:

   - When creating a new basket group: The logged-in user's library
     should be pre-selected.

   - When editing a basket group which has a library defined for either
     the billing or delivery places, the correct library should be
     pre-selected.

   - When editing a basket group which has no library defined for either
     the billing or delivery place there should be no library
     pre-selected (the "--" option should be pre-selected).

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>