Formatting empty where clause with trailing_comma = "Never" leaves trailing whitespace, causing an error.

[Esper89]

Formatting the following code with trailing_comma = "Never" will leave trailing whitespace:

pub struct Matrix<T, const R: usize, const C: usize>
where
    [T; R * C]: 
{
    contents: [T; R * C]
}

    [T; R * C]: 
               ^ right here

Without trailing_comma = "Never", the line is formatted like this:

    [T; R * C]: ,

The trailing whitespace causes rustfmt has failed to format, resulting in the whole file not being formatted.

A workaround is to leave a comment at the end of the line like this:

    [T; R * C]:  //

[calebcartwright]

Thanks for the report!