bizarre string indentation with format_strings and wrap_comments

[AaronKutch]

On the latest rustfmt with a .rustfmt.toml of

format_strings = true
wrap_comments = true

and the code

macro_rules! test {
    () => {
        fn from() {
            None.expect(
                "We asserted that `buffer.len()` is exactly `$n` so we can expect \
                `ApInt::from_iter` to be successful.",
            )
        }
    };
}

This gets reformatted to

macro_rules! test {
    () => {
        fn from() {
            None.expect(
                "We asserted that `buffer.len()` is exactly `$n` so we can expect \
         `ApInt::from_iter` to be successful.",
            )
        }
    };
}

Because there is a space in there and not a whole number of indentations, I think it is some off-by-one error in some code that deals with the indentations.

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[yodaldevoid]

This bug doesn't seem to require wrap_comments now, if it ever really did.

A better title would probably be "bizarre string indentation in macro defs with format_strings".