ldb:tests: Avoid that the debug function overwrites memory

ldb:tests: Avoid that the debug function overwrites memory

We are setting ldb_debug_string() as the ldb debug function. The context
we give it is only valid as long as we're in that function.

On failure, we jump to the teardown function. The pointer for
debug_string isn't valid anymore, but the ldb debug system still points
to that address, and when we store the location of the allocated string,
we overwrite memory, in that case something from talloc and a
talloc_free() then jumps into the nirvana.

Thanks to Florian Weimer who helped debugging this.

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Isaac Boukris <iboukris@samba.org>