www/tinytinyhttpd: Unbreak with Clang 6

c++ -DHAVE_CONFIG_H -I. -O2 -pipe -fstack-protector -fno-strict-aliasing -D_THREAD_SAFE -pthread -D_REENTRANT -MT httpd.o -MD -MP -MF .deps/httpd.Tpo -c -o httpd.o httpd.cxx
httpd.cxx:1019:21: error: assigning to 'int' from incompatible type 'nullptr_t'

res_info->write = NULL;
                  ^~~~

httpd.cxx:1734:8: error: no matching function for call to 'sendfile'

if (sendfile(msgsock, res_info->read, NULL, total, NULL, NULL, 0) == 0) sent = total;
    ^~~~~~~~

http://beefy12.nyi.freebsd.org/data/head-amd64-default/p475044_s336572/logs/tinytinyhttpd-0.0.11.log

PR: 230890
Submitted by: tobik
Approved by: smatsui@karashi.org (maintainer timeout, 2 weeks)