Bug 18403: Deal with the DB user

Bug 18403: Deal with the DB user

On first login, Koha explodes before the logged in user does not exist
in DB.
This patch deals with that by adding several checks when it's needed.

Test plan:
Use the DB user to create a superlibrarian user.
The DB user should no be allowed to do anything else.

Signed-off-by: Signed-off-by: Jon McGowan <jon.mcgowan@ptfs-europe.com>
Bug 18403: Fix patron creation

memberentry.pl can be called to create a new patron, in that case the
patron does not exist yet.

Signed-off-by: Signed-off-by: Jon McGowan <jon.mcgowan@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>