Bug 6116: Adding a child patron

Bug 6116: Adding a child patron

When adding a patron who is a child, the default library is not set when defining a guarantor, this patch corrects the problem.
More, for children with no guarantors, the default branch is the editing branch.

BibLibre MT5795

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
(cherry picked from commit 36f526a9a8dab77259b35f5ab4697575d9a10f44)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>