secure/bidirule: add continue for clarity

otherwise has no effect

Change-Id: Ie034c6441d36e97267e3d005e0e14bb082fbee17
Reviewed-on: https://go-review.googlesource.com/63792
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>

secure/bidirule/bidirule.go

diff --git a/secure/bidirule/bidirule.go b/secure/bidirule/bidirule.go
index 5d0f99c..0e6b858 100644
--- a/secure/bidirule/bidirule.go
+++ b/secure/bidirule/bidirule.go
@@ -155,6 +155,7 @@
 		e, sz := bidi.LookupString(s[i:])
 		if sz == 0 {
 			i++
+			continue
 		}
 		c := e.Class()
 		if c == bidi.R || c == bidi.AL || c == bidi.AN {

secure/bidirule/bidirule_test.go

diff --git a/secure/bidirule/bidirule_test.go b/secure/bidirule/bidirule_test.go
index 2398a6e..4b6c612 100644
--- a/secure/bidirule/bidirule_test.go
+++ b/secure/bidirule/bidirule_test.go
@@ -717,6 +717,11 @@
 		dir: bidi.LeftToRight,
 		n:   len("FAX\u2a77\U0001d186"),
 		err: ErrInvalid,
+	}, {
+		in:  "\x80\u0660",
+		dir: bidi.RightToLeft,
+		n:   0,
+		err: ErrInvalid,
 	}},
 }