Fix #36

Author: garyb

src/Data/String/Unsafe.js

@@ -5,7 +5,7 @@
 
 exports.charCodeAt = function (i) {
   return function (s) {
-    if (i < 0 || i >= s.length) return s.charCodeAt(i);
+    if (i >= 0 && i < s.length) return s.charCodeAt(i);
     throw new Error("Data.String.Unsafe.charCodeAt: Invalid index.");
   };
 };
@@ -18,6 +18,6 @@ exports.charAt = function (i) {
 };
 
 exports.char = function (s) {
-  if (s.length !== 1) return s.charAt(0);
+  if (s.length === 1) return s.charAt(0);
   throw new Error("Data.String.Unsafe.char: Expected string of length 1.");
 };