date: complain if there are extraneout arguments

diff --git a/coreutils/date.c b/coreutils/date.c
index 2aecbaa..2c61aa6 100644
--- a/coreutils/date.c
+++ b/coreutils/date.c
@@ -79,6 +79,8 @@
 	if (!(opt & (DATE_OPT_SET | DATE_OPT_DATE))) {
 		opt |= DATE_OPT_SET;
 		date_str = argv[0]; /* can be NULL */
+	} else if (argv[0]) {
+		bb_show_usage();
 	}
 
 	/* Now we have parsed all the information except the date format