ljpeg: Fix bits != 8 or 16 support

Fixes 2nd half of Ticket889

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

libavcodec/mjpegdec.c

@@ -804,6 +804,7 @@ static int ljpeg_decode_yuv_scan(MJpegDecodeContext *s, int predictor, int point
 
                         if (s->interlaced && s->bottom_field)
                             ptr += linesize >> 1;
+                        pred &= (-1)<<(8-s->bits);
                         *ptr= pred + (dc << point_transform);
                         }else{
                             ptr16 = s->picture.data[c] + 2*(linesize * (v * mb_y + y)) + 2*(h * mb_x + x); //FIXME optimize this crap
@@ -823,6 +824,7 @@ static int ljpeg_decode_yuv_scan(MJpegDecodeContext *s, int predictor, int point
 
                             if (s->interlaced && s->bottom_field)
                                 ptr16 += linesize >> 1;
+                            pred &= (-1)<<(16-s->bits);
                             *ptr16= pred + (dc << point_transform);
                         }
                         if (++x == h) {
@@ -856,11 +858,13 @@ static int ljpeg_decode_yuv_scan(MJpegDecodeContext *s, int predictor, int point
                         ptr = s->picture.data[c] + (linesize * (v * mb_y + y)) + (h * mb_x + x); //FIXME optimize this crap
                         PREDICT(pred, ptr[-linesize-1], ptr[-linesize], ptr[-1], predictor);
 
+                        pred &= (-1)<<(8-s->bits);
                         *ptr= pred + (dc << point_transform);
                         }else{
                             ptr16 = s->picture.data[c] + 2*(linesize * (v * mb_y + y)) + 2*(h * mb_x + x); //FIXME optimize this crap
                             PREDICT(pred, ptr16[-linesize-1], ptr16[-linesize], ptr16[-1], predictor);
 
+                            pred &= (-1)<<(16-s->bits);
                             *ptr16= pred + (dc << point_transform);
                         }
                         if (++x == h) {