avcodec/huffyuvdec: Fix fill value for truncated bitstreams

Found-by: Christophe Gisquet <christophe.gisquet@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/huffyuvdec.c

@@ -632,7 +632,7 @@ static void decode_422_bitstream(HYuvContext *s, int count)
         }
         for (; i < count; i++)
             s->temp[0][2 * i    ] = s->temp[1][i] =
-            s->temp[0][2 * i + 1] = s->temp[2][i] = 128;
+            s->temp[0][2 * i + 1] = s->temp[2][i] = 0;
     } else {
         for (i = 0; i < count; i++) {
             READ_2PIX(s->temp[0][2 * i    ], s->temp[1][i], 1);