ldb: Fix memory leak on module context

ldb: Fix memory leak on module context

Introduced in e8cdacc509016d9273d63faf334d9f827585c3eb

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13459

Signed-off-by: Lukas Slebodnik <lslebodn@fedoraproject.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Fri Jun  1 11:10:24 CEST 2018 on sn-devel-144

(cherry picked from commit d161aa3522576545d269208426bb0014ee2ab35f)