Fix more to a non-tty.

And add a test.
diff --git a/toys/pending/more.c b/toys/pending/more.c
index 55bed36..59b5c61 100644
--- a/toys/pending/more.c
+++ b/toys/pending/more.c
@@ -63,7 +63,7 @@
 static void do_cat_operation(int fd, char *name)
 {
   if (toys.optc > 1) show_file_header(name);
-  xsendfile(0, 1);
+  xsendfile(fd, 1);
 }
 
 void more_main()