fixed parse error when broken comments

Author: rhiokim

index.js

@@ -157,7 +157,7 @@ module.exports = function(css, options){
     if ('/' != css.charAt(0) || '*' != css.charAt(1)) return;
 
     var i = 2;
-    while (null != css.charAt(i) && ('*' != css.charAt(i) || '/' != css.charAt(i + 1))) ++i;
+    while ('' !== css.charAt(i) && ('*' != css.charAt(i) || '/' != css.charAt(i + 1))) ++i;
     i += 2;
 
     var str = css.slice(2, i - 2);