make ExUtilLoadWebP() accept NULL bitstream param.

Change-Id: Ifce379873ca39e46d011a1cb829beab89de5f15d
diff --git a/examples/example_util.c b/examples/example_util.c
index 8bfff69..d3dbc61 100644
--- a/examples/example_util.c
+++ b/examples/example_util.c
@@ -131,8 +131,13 @@
                    const uint8_t** data, size_t* data_size,
                    WebPBitstreamFeatures* bitstream) {
   VP8StatusCode status;
+  WebPBitstreamFeatures local_features;
   if (!ExUtilReadFile(in_file, data, data_size)) return 0;
 
+  if (bitstream == NULL) {
+    bitstream = &local_features;
+  }
+
   status = WebPGetFeatures(*data, *data_size, bitstream);
   if (status != VP8_STATUS_OK) {
     free((void*)*data);