Security fix, CVE-2017-14491, DNS heap buffer overflow.
    
    Further fix to 0549c73b7ea6b22a3c49beb4d432f185a81efcbc
    Handles case when RR name is not a pointer to the question,
    only occurs for some auth-mode replies, therefore not
    detected by fuzzing (?)
    
    Signed-off-by: Petr Menšík <pemensik@redhat.com>