updated fix for issue #194, wma import problems under Mac OSX/Linux

As requested I removed the code that was using the const variable, thus preventing windows build to break.  Original pull request can be found here: https://github.com/nightingale-media-player/nightingale-hacking/pull/223 

Steps to verify if 'fix' worked correctly: 

1. Took some of my .mp3's and converted them to .wma, using this website, http://media.io/
2. File > Import media, adds .wma to Library properly.
3. File > Open File .. also works correctly.
4. If you have Watch Folders option enabled, moving the .wma files into the watched directory or dragging the .wma file into the library view, will correctly import the .wma file into nightingale.
5. Playback works on Linux build.

We need someone to verify this on a mac!!! Please and thanks!

Thanks to @rsjtdrjgfuzkfg for helping out.