Inserted a missing string encoding check in lastIndexOf.

src/string.js

Index: src/string.js
diff --git a/src/string.js b/src/string.js
index 50531822be15f65ec9718c208de357252274c4cb..5c20dde5eb59114852b7514e9ccc210a64b3e4e9 100644
--- a/src/string.js
+++ b/src/string.js
@@ -149,7 +149,7 @@ function StringLastIndexOf(pat /* position */) {  // length == 1
         position = 0;
       }
       if (position + patLength < subLength) {
-        index = position
+        index = position;
       }
     }
   }