Fix an overflow in the predictor.

fixes issue 636
Patch by Jai.

Originally committed as revision 16007 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/alacenc.c

@@ -253,7 +253,8 @@ static void alac_linear_predictor(AlacEncodeContext *s, int ch)
 
             sum >>= lpc.lpc_quant;
             sum += samples[0];
-            residual[i] = samples[lpc.lpc_order+1] - sum;
+            residual[i] = (samples[lpc.lpc_order+1] - sum) << (32 - s->write_sample_size) >>
+                          (32 - s->write_sample_size);
             res_val = residual[i];
 
             if(res_val) {