Allow working on untitled documents

[bscan]

Currently the language server does not work on unsaved buffers. The following Stackoverflow questions shows how to enable this, but I suspect there are many other pieces of the code that assume a real file exists. Although I suppose there's a possibility this is a very easy change and is primarily about testing.

https://stackoverflow.com/questions/52625924/how-can-i-let-language-server-watch-the-untitled-1-file-change