Reference fix for CVE-2018-13458, CVE-2018-13457 and CVE-2018-13441

Specific to nagios4 code fixed with same commit for the three issues
(NULL ppointer dereference in thee functions qh_echo, qh_help and
qh_core).

https://gist.github.com/fakhrizulkifli/8df4a174158df69ebd765f824bd736b8