godef not working for UTF-8 BOM encoded files

[boxu-zhang]

I'm using Vscode-go to develop. Today, I found a strange problem that godef tool not working for those files encoded with UTF-8 BOM. And I debugged the problem with godef source. It turned out that the parse shows 'illegal content U+FFEF' which is not very accurate but still helpful. I followed the lead and finally find out it's all about the UTF-8 BOM. After I changed the source file to UTF-8 without BOM, everything goes fine.