PVS-Studio warning V593 for LibRaw

int main(int argc, char *argv[])
{
  int ret;
  ....
  if( (ret = RawProcessor.open_buffer(iobuffer,st.st_size)
             != LIBRAW_SUCCESS))
  {
    fprintf(stderr,"Cannot open_buffer %s: %s\n",
      argv[arg],libraw_strerror(ret));
    free(iobuffer);
    continue;
  }
  ....
}

This suspicious code was found in LibRaw project by PVS-Studio static code analyzer.
Warning message is:
V593 Consider reviewing the expression of the 'A = B != C' kind. The expression is calculated as following: 'A = (B != C)'. dcraw_emu.cpp 468

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/