Fixed incorrect call to DestroyImage reported in #491.
MagickExport MagickBooleanType IsImageObject(const Image *image)
{
  register const Image
    *p;

  assert(image != (Image *) NULL);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"...");
  for (p=image; p != (Image *) NULL; p=GetNextImageInList(p))
    if (p->signature != MagickSignature)
      return(MagickFalse);
  return(MagickTrue);
}

MagickExport MagickBooleanType IsImageObject(const Image *image)
{
  register const Image
    *p;

  assert(image != (Image *) NULL);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"...");
  for (p=image; p != (Image *) NULL; p=GetNextImageInList(p))
    if (p->signature != MagickSignature)
      return(MagickFalse);
  return(MagickTrue);
}
