vpxdec: don't require -o with --noblit

Specifiying the output file is meaningless when we're not writing to
it.

Change-Id: I271e1d3ae1994d79f0773747477124600f98ca58
diff --git a/vpxdec.c b/vpxdec.c
index 79b8c62..48a36cd 100644
--- a/vpxdec.c
+++ b/vpxdec.c
@@ -813,7 +813,7 @@
     }
 
     /* Make sure we don't dump to the terminal, unless forced to with -o - */
-    if(!outfile_pattern && isatty(fileno(stdout)) && !do_md5)
+    if(!outfile_pattern && isatty(fileno(stdout)) && !do_md5 && !noblit)
     {
         fprintf(stderr,
                 "Not dumping raw video to your terminal. Use '-o -' to "