Core: allow strings without null-termination in ngx_parse_url().

Core: allow strings without null-termination in ngx_parse_url().

This fixes buffer over-read while using variables in the "proxy_pass",
"fastcgi_pass", "scgi_pass", and "uwsgi_pass" directives, where result
of string evaluation isn't null-terminated.

Found with MemorySanitizer.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>