Fixes some var-args missing va_start/end

This was introduced in

     apache#1299

But, the good news is that this has not been part of a release.

Author: Katsutoshi Ikenoya

proxy/http/HttpBodyFactory.h

@@ -166,10 +166,14 @@ class HttpBodyFactory
     if (format) {
       // The length from ink_bvsprintf includes the trailing NUL, so adjust the final
       // length accordingly.
+      va_start(ap, format);
       int l = ink_bvsprintf(nullptr, format, ap);
+      va_end(ap);
       if (l <= max_buffer_length) {
-        msg                      = (char *)ats_malloc(l);
+        msg = (char *)ats_malloc(l);
+        va_start(ap, format);
         *resulting_buffer_length = ink_bvsprintf(msg, format, ap) - 1;
+        va_end(ap);
       }
     }
     return msg;