fix bug in scalable_decoder

file_is_obu( ) was changed so that the filename of the bitstream
must be assigned to input_ctx

BUG=aomedia:1501

Change-Id: I6e248483a98d98bea6b3191a32335e3d91c6ef8b

examples/scalable_decoder.c

diff --git a/examples/scalable_decoder.c b/examples/scalable_decoder.c
index 92b6f46..49f9728 100644
--- a/examples/scalable_decoder.c
+++ b/examples/scalable_decoder.c
@@ -122,6 +122,7 @@
   if (!(inputfile = fopen(argv[1], "rb")))
     die("Failed to open %s for read.", argv[1]);
   input.aom_input_ctx->file = inputfile;
+  input.aom_input_ctx->filename = argv[1];
 
   decoder = get_aom_decoder_by_index(0);
   printf("Using %s\n", aom_codec_iface_name(decoder->codec_interface()));