PVS-Studio warning V595 for MAME

static void stv_vdp2_drawgfxzoom(...,
  const gfx_element *gfx, ...)
{
  ...
  if (gfx->pen_usage &&
      transparency == STV_TRANSPARENCY_PEN)
  {
    ...
  }

  if( gfx )
  {
    ...
  }
  ...
}

This suspicious code was found in MAME project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'gfx' pointer was utilized before it was verified against nullptr. Check lines: 2457, 2483.  stvvdp2.c 2457

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/