PVS-Studio warning V595 for OpenSSL

#define bn_wexpand(a,words) \
  (((words) <= (a)->dmax)?(a):bn_expand2((a),(words)))

static int ubsec_dh_generate_key(DH *dh)
{
  ....
  if(bn_wexpand(pub_key, dh->p->top) == NULL) goto err;
  if(pub_key == NULL) goto err;
  ....
}

The 'pub_key' pointer was dereferenced in bn_wexpand macros.

This suspicious code was found in OpenSSL project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'pub_key' pointer was utilized before it was verified against nullptr. Check lines: 951, 952. e_ubsec.c 951

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/