Code: check_interlace_type(int PNG_CONST interlace_type)
 {
    if (interlace_type != PNG_INTERLACE_NONE)
    {
       /* This is an internal error - --interlace tests should be skipped, not
       * attempted.
       */
      fprintf(stderr, "pngvalid: no interlace support\n");

       exit(99);
    }
 }

Commit Message: DO NOT MERGE Update libpng to 1.6.20

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

CWE ID: 
check_interlace_type(int PNG_CONST interlace_type)
check_interlace_type(int const interlace_type)
 {
   /* Prior to 1.7.0 libpng does not support the write of an interlaced image
    * unless PNG_WRITE_INTERLACING_SUPPORTED, even with do_interlace so the
    * code here does the pixel interlace itself, so:
    */
    if (interlace_type != PNG_INTERLACE_NONE)
    {
       /* This is an internal error - --interlace tests should be skipped, not
       * attempted.
       */
      fprintf(stderr, "pngvalid: no interlace support\n");

       exit(99);
    }
 }
