Bug 3629 : search limit by group is not OK

Bug 3629 : search limit by group is not OK

MT4491 : limitation by library group

- the group list was not displayed in OPAC (even if everything else was here
- the group limit was not working due to a missing ()

author=jean et group=droit" resulted in:
author=jean and branch=b1 or branch=b2 or branch=b3
that is wrong (executed from left to right)

the fix add () to have :
author=jean and (branch=b1 or branch=b2 or branch=b3)
that is OK

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>