DO NOT MERGE Update libpng to 1.6.20

BUG:23265085
Change-Id: I85199805636d771f3597b691b63bc0bf46084833
(cherry picked from commit bbe98b40cda082024b669fa508931042eed18f82)

file_setpos(struct file *file, const fpos_t *pos)
{
 if (fsetpos(file->file, pos))
 {
      perror(file->file_name);
      stop(file, READ_ERROR_CODE, "fsetpos");
 }
}

file_setpos(struct file *file, const fpos_t *pos)
{
 if (fsetpos(file->file, pos))
 {
      perror(file->file_name);
      stop(file, READ_ERROR_CODE, "fsetpos");
 }
}
