Fix a crash when running as systemd service

- Fix a NULL dereference if a signal is raised in the constructor of the
class InspIRCd
- Resolve the parent's process exit code being SIGTERM=15 and typically not
EXIT_SUCCESS thus

A combination of the two caused crashes when running as systemd unit.
m_showwhois Require 2 parameters for WHOISNOTICE
m_httpd Close all open http sockets on unload