PVS-Studio warning V516 for Audacity

int sf_error (SNDFILE *sndfile)
{
  ...
  if (! sndfile)
  {
    if (sf_error != 0)
      return sf_errno ;
    return 0 ;
  } ;
  ...
}

Strange code. Perhaps there should be (sf_errno != 0). But why not simply write "return sf_errno;" then?

This suspicious code was found in Audacity project by PVS-Studio static code analyzer.
Warning message is:
V516 Consider inspecting an odd expression. Non-null function pointer is compared to null: 'sf_error != 0'. libsndfile sndfile.c 491

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/