ldb: Add test with == true or false to boolean if statements in ldb_dn_explode()

ldb: Add test with == true or false to boolean if statements in ldb_dn_explode()

This is beyond the normal level of clarity we expect in Samba, and is of course
rudundent, but this is a complex routine that has confusing tests, some of
pointers and some of boolean state values.

This tries to make the code as clear as possible pending a more comprehensive
rewrite.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14049

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
(cherry picked from commit 52bd2dde5ae809ecc115f7087e367327f4771e73)