Change the y4m buffer allocation size

This attempts to fix issue #847

Change-Id: Ifa2f96b6b33624004272d83363e089b5b4dc5626

y4minput.c

@@ -975,9 +975,9 @@ int y4m_input_open(y4m_input *_y4m, FILE *_fin, char *_skip, int _nskip,
                      + 2 * ((_y4m->pic_w + _y4m->dst_c_dec_h - 1) / _y4m->dst_c_dec_h) *
                      ((_y4m->pic_h + _y4m->dst_c_dec_v - 1) / _y4m->dst_c_dec_v);
   if (_y4m->bit_depth == 8)
-    _y4m->dst_buf = (unsigned char *)malloc(_y4m->dst_buf_sz);
+    _y4m->dst_buf = (unsigned char *)malloc(_y4m->dst_buf_read_sz);
   else
-    _y4m->dst_buf = (unsigned char *)malloc(2 * _y4m->dst_buf_sz);
+    _y4m->dst_buf = (unsigned char *)malloc(2 * _y4m->dst_buf_read_sz);
 
   if (_y4m->aux_buf_sz > 0)
     _y4m->aux_buf = (unsigned char *)malloc(_y4m->aux_buf_sz);