No check if document.getElementById ("lang") exists at all, resulting in a type error

[cboulanger]

Hi,

Thank you for NN-Forum. I am using it successfully in a plugin for a bibliographic application:

https://github.com/cboulanger/bibliograph/tree/master/bibliograph/plugins/nnforum

I had to tweak it a liitle bit to make it work for me(sorry, didn't clone it, just used the zip, but marked all the changes)

There is one thing that striked me as a bug, see

https://github.com/cboulanger/bibliograph/blob/master/bibliograph/plugins/nnforum/services/www/themes/greyscale/index.html#L212

document.getElementById ("lang") is not present by default, thereby resulting in a type error. I had to add if ( document.getElementById ("lang") ) here and in the other theme files.

Best,
Christian