Bug in BLIT_TRANSL_888(SDL-2.0.3)

I think there is tow problem in BLIT_TRANSL_888. One is Blue value maybe
effect Red. The other is Alpha, it is always 255.

Blue value maybe effect Red. When dst’s B is less then src’s B, will result
in dst’ R to minus 1.

Because here cannot use image, this post describes it more detail.
http://www.freeors.com/bbs/forum.php?mod=viewthread
<http://www.freeors.com/bbs/forum.php?mod=viewthread&tid=23430&extra=page%3D
1> &tid=23430&extra=page%3D1