Unicode COMM tags are not written correctly

[Mbucari]

When writing a unicode COMM tag, the null tag description is missing the BOM prefix. https://github.com/Corey-M/NAudio.Lame/blob/ed76eb646de2c8fc2826ce8fedc054df09500e1d/LameDLLWrap/LibMp3Lame.cs#L614

To correct this, do something like:

return CheckResult(NativeMethods.id3tag_set_comment_utf16(context, "zxx", UCS2.GetBytes(string.Empty), data));