segfault fix patch by (Juergen Keil <jk at tools dot de>)

Originally committed as revision 1073 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h263.c

@@ -4644,6 +4644,10 @@ int intel_h263_decode_picture_header(MpegEncContext *s)
         skip_bits(&s->gb, 8);
     }
     s->f_code = 1;
+
+    s->y_dc_scale_table=
+    s->c_dc_scale_table= ff_mpeg1_dc_scale_table;
+
     return 0;
 }