Core: fixed segfault with null in wildcard hash names.
Core: fixed segfault with null in wildcard hash names.

A configuration like

    server { server_name .foo^@; }
    server { server_name .foo; }

resulted in a segmentation fault during construction of server names hash.

Reported by Markus Linnala.
Found with afl-fuzz.

firebase/nginx,firebase/nginx,firebase/nginx,firebase/nginx