idviews: clear intermediate target DN in all cases
When processing a search request, slapi-nis attempts to detect an ID
View lookup. A target DN is modified by extracting an ID view name. This
temporary string is freed in the successful case but left unotouched if
ID View wasn't requested. As a result, small leaks on each search
request accumulate and a memory can get lost.
Resolves: rhbz#1866113
Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>