fix android JSON.parse(null) bug

    bug fix for Andoid JSON.parse bug

    error message is

    ```
    Uncaught illegal access at file:///android_asset/www/plugins/memory.enchant.
js:667"
    ```

    See also for same bug

    Android + JSON.parse(NULL) = Uncaught illegal access · Issue #48 · brianlero
ux/lawnchair
    https://github.com/brianleroux/lawnchair/issues/48

    in Japanese
    http://metamosoft.hatenablog.com/entry/2013/06/16/143156?_ga=1.145227508.159
6586333.1367849780
Merge pull request #255 from hshimo/fix/androidJsonParseBug

fix android JSON.parse(null) bug