mjpegdec: make sure we dont interpret things after the bitstream buffer as resync marker

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

libavcodec/mjpegdec.c

@@ -898,9 +898,9 @@ static int mjpeg_decode_scan(MJpegDecodeContext *s, int nb_components, int Ah, i
             if (s->restart_interval && show_bits(&s->gb, i)  == (1<<i)-1){ /* skip RSTn */
                 int pos= get_bits_count(&s->gb);
                 align_get_bits(&s->gb);
-                while(show_bits(&s->gb, 8) == 0xFF)
+                while(get_bits_count(&s->gb) < s->gb.size_in_bits && show_bits(&s->gb, 8) == 0xFF)
                     skip_bits(&s->gb, 8);
-                if((get_bits(&s->gb, 8)&0xF8) == 0xD0){
+                if(get_bits_count(&s->gb) < s->gb.size_in_bits && (get_bits(&s->gb, 8)&0xF8) == 0xD0){
                     for (i=0; i<nb_components; i++) /* reset dc */
                         s->last_dc[i] = 1024;
                 }else{