SSL/TLS code.
The negative return value from X509_verify_cert() can only occur if no
-certificate is set in B<ctx> (due to a programming error) or if a retry
+certificate is set in B<ctx> (due to a programming error); if X509_verify_cert()
+twice without reinitialising B<ctx> in between; or if a retry
operation is requested during internal lookups (which never happens with
standard lookup methods). It is however recommended that application check
for <= 0 return value on error.