Bug 18947: LDAP - do not assume anonymous bind if no user or password

Bug 18947: LDAP - do not assume anonymous bind if no user or password

To test:
Ideally tested on a working ldap server with bind by auth and no
anonymous bind
1  - Define an LDAP config with bind by auth
2  - Don't define user/pass
3  - Define anonymous_bind = 0
4  - Attempt bind by auth
5  - Error is something like:
LDAP search failed to return object : XXXXXXXXX: LdapErr: XXXX-XXXXXX,
     comment: In order to perform this operation a successful bind must
     be completed on the connection., data 0, v2580 at
     /usr/share/koha/lib/C4/Auth_with_ldap.pm line 102.
6  - Define user/pass
7  - Now bind by auth should work
8  - remove user/pass
9  - Apply patch
10 - Attempt again
11 - Bind by auth shoudl succeed

prove -v t/db_dependent/Auth_with_ldap.t

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 8eed0466381435a0426fe9c2ea75fa295d906533)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>