Fixed segfaults on corruped smacker streams in the decoder.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit d07ac1853d)

libavcodec/smacker.c

@@ -660,6 +660,8 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
     } else { //8-bit data
         for(i = stereo; i >= 0; i--)
             pred[i] = get_bits(&gb, 8);
+        if (stereo + unp_size > data_size)
+            return -1;
         for(i = 0; i < stereo; i++)
             *samples++ = (pred[i] - 0x80) << 8;
         for(i = 0; i < unp_size; i++) {