svq1dec: dont export the qscale table.

SVQ1 has no qscales so the table is of no use, and it triggers a bug as
SVQ1 does not maintain the size of the table properly causing a crash.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/svq1dec.c

@@ -699,6 +699,7 @@ static int svq1_decode_frame(AVCodecContext *avctx, void *data,
     }
 
     *pict = s->current_picture.f;
+    pict->qscale_table = NULL;
 
     ff_MPV_frame_end(s);