avcodec/mjpegdec: fix green line at the bottom with upscale v

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit f0d4f00f24)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mjpegdec.c

@@ -2130,7 +2130,7 @@ the_end:
             for (i = s->height - 1; i; i--) {
                 uint8_t *src1 = &((uint8_t *)s->picture_ptr->data[p])[i / 2 * s->linesize[p]];
                 uint8_t *src2 = &((uint8_t *)s->picture_ptr->data[p])[(i + 1) / 2 * s->linesize[p]];
-                if (src1 == src2) {
+                if (src1 == src2 || i == s->height - 1) {
                     memcpy(dst, src1, w);
                 } else {
                     for (index = 0; index < w; index++)