Fix a segmentation fault in slowhttptest.

slowhttptest didn't check that the argument passed to freeaddrinfo(3)
was not NULL, which resulted in a segmentation fault.

OK jca@

www/slowhttptest/Makefile

@@ -1,10 +1,11 @@
-# $OpenBSD: Makefile,v 1.15 2019/11/02 08:48:07 fcambus Exp $
+# $OpenBSD: Makefile,v 1.16 2019/11/08 15:59:28 fcambus Exp $
 
 COMMENT=	test tool for slow HTTP reads/posts
 
 GH_ACCOUNT=	shekyan
 GH_PROJECT=	slowhttptest
 GH_TAGNAME=	v1.8.1
+REVISION=	0
 
 CATEGORIES=	www security
 

www/slowhttptest/patches/patch-src_slowhttptest_cc

@@ -0,0 +1,18 @@
+$OpenBSD: patch-src_slowhttptest_cc,v 1.3 2019/11/08 15:59:28 fcambus Exp $
+
+Check that the argument passed to freeaddrinfo(3) is not NULL.
+
+Index: src/slowhttptest.cc
+--- src/slowhttptest.cc.orig
++++ src/slowhttptest.cc
+@@ -152,7 +152,9 @@ SlowHTTPTest::SlowHTTPTest(int delay, int duration, 
+ }
+ 
+ SlowHTTPTest::~SlowHTTPTest() {
+-  freeaddrinfo(addr_);
++  if (addr_) {
++    freeaddrinfo(addr_);
++  }
+ 
+   for(std::vector<StatsDumper*>::iterator i = dumpers_.begin();
+        i != dumpers_.end(); ++i) {