Fix almost-10-year-old lastIndex bug reported by Sjoerd Visscher <sjoerd@w3future.com> (283477, r=me).

js/src/jsstr.c

@@ -1039,8 +1039,8 @@ str_lastIndexOf(JSContext *cx, JSObject *obj, uintN argc, jsval *argv,
             d = js_DoubleToInteger(d);
             if (d < 0)
                 i = 0;
-            else if (d > textlen - patlen)
+            else if (d > textlen)
-                i = textlen - patlen;
+                i = textlen;
             else
                 i = (jsint)d;
         }