Ranged index search memory leak

Closed Andrew Bartlett requested to merge samba-team/devel/samba:abartlet/ldb-memory-leak into master

Address a memory leak seen in the ranged index code, which speeds up searches of <= and >=.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14299 REF: https://lists.samba.org/archive/samba/2020-February/228380.html