Clear REDIRECT flag when it isn't needed

Clear REDIRECT flag when it isn't needed

The NS_QUERYATTR_REDIRECT flag is set when processing a recursive
NXDOMAIN redirection lookup, so that if that lookup also returns
NXDOMAIN we don't end up looping.

Previously, the flag was left active after use, but if the
same client triggered a subsequent recursive lookup (for example,
in the filter-aaaa plugin), then the wrong branch could be reached
in query_resume(), potentially leading to an assertion failure.  This
has been fixed.

(cherry picked from commit 3ff00183086f304c71076a069376e37692a7c9ff)