Fix function call error and NULL path send out

Check pointer to avoid NULL pointer input to strlen()
Auto replace NULL path to "/" (As Firefox`s implementation)

Author: StevenChen8759

htstress.c

@@ -487,9 +487,12 @@ int main(int argc, char *argv[])
     /* prepare request buffer */
     if (!host)
         host = node;
-    outbufsize = strlen(rq) + sizeof(HTTP_REQUEST_FMT) + strlen(host);
+    outbufsize = sizeof(HTTP_REQUEST_FMT) + strlen(host);
+    outbufsize += rq ? strlen(rq) : 1;
+
     outbuf = malloc(outbufsize);
-    outbufsize = snprintf(outbuf, outbufsize, HTTP_REQUEST_FMT, rq, host);
+    outbufsize = rq ? snprintf(outbuf, outbufsize, HTTP_REQUEST_FMT, rq, host)
+                    : snprintf(outbuf, outbufsize, HTTP_REQUEST_FMT, "/", host);
 
     ticks = max_requests / 10;