SongChordTemplate2014.AddChordIds can throw a NullReferenceException

Apparently, in some official arrangements there are chord templates in the manifest that are not contained in the sng. You can easily hit the bug by unpacking (and generating xmls) the songs.psarc. As far as I can tell it's safe to disregard these extra chord templates in the manifest, so I added a check for null in the function.