fix range on invalid utf8 bug

R=r
DELTA=42  (21 added, 20 deleted, 1 changed)
OCL=34328
CL=34333

src/pkg/runtime/rune.c

@@ -161,8 +161,9 @@ bad:
 	*rune = Bad;
 	return 1;
 badlen:
+	// was return 0, but return 1 is more convenient for the runtime.
 	*rune = Bad;
-	return 0;
+	return 1;
 
 }