Formatter appends comma to empty tuple that contains a comment

[achowd32]

Describe the bug
This is an edge case where the formatter messes up an empty tuple that contains a comment.

To Reproduce
Consider the following code:

fn tup() -> () {
   (
       // this is an empty tuple
   )
}

Running this through the formatter generates

fn tup() -> () {
   (
       , // this is an empty tuple
   )
}

Notice the addition of the stray comma, which the interpreter is not able to parse.
Expected behavior
The comma should not be added.

Additional context
I think this is a fairly simple bug, I would be interested in resolving this is maintainers agree it is an issue.

[dplassgit]

It's a small edge case, but it's fine if you want to pursue it.