Setup sb_size when decoding intra_only frame

This fixes decoder's capability to start decoding
bitstream from non-KEY intra_only frame.

BUG=aomedia:816

Change-Id: Iecd5add418590119f59a51acd7208eb08cb17042

av1/decoder/decodeframe.c

@@ -4803,6 +4803,7 @@ static size_t read_uncompressed_header(AV1Decoder *pbi,
 
       pbi->refresh_frame_flags = aom_rb_read_literal(rb, REF_FRAMES);
       setup_frame_size(cm, rb);
+      setup_sb_size(cm, rb);
       if (pbi->need_resync) {
         memset(&cm->ref_frame_map, -1, sizeof(cm->ref_frame_map));
         pbi->need_resync = 0;