segfault fix

Originally committed as revision 418 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h263.c

@@ -359,8 +359,13 @@ void mpeg4_encode_mb(MpegEncContext * s,
                     uint8_t *p_pic= s->new_picture[0] + offset;
                     s->mb_skiped=1;
                     for(i=0; i<s->max_b_frames; i++){
-                        uint8_t *b_pic= s->coded_order[i+1].picture[0] + offset;
-                        int diff= pix_abs16x16(p_pic, b_pic, s->linesize);
+                        uint8_t *b_pic;
+                        int diff;
+
+                        if(s->coded_order[i+1].pict_type!=B_TYPE) break;
+
+                        b_pic= s->coded_order[i+1].picture[0] + offset;
+                        diff= pix_abs16x16(p_pic, b_pic, s->linesize);
                         if(diff>s->qscale*70){
                             s->mb_skiped=0;
                             break;

libavcodec/mpegvideo.c

@@ -645,6 +645,7 @@ void reorder_input(MpegEncContext *s, AVPicture *pict)
         s->coded_order[j]= s->coded_order[j+1];
     }
     s->coded_order[j].picture[0]= s->coded_order[j].picture[1]= s->coded_order[j].picture[2]= NULL; //catch uninitalized buffers
+    s->coded_order[j].pict_type=0;
 
     switch(s->input_pict_type){
     default: