Comment indentation is always changed

[mqudsi]

With both normalize_comments and wrap_comments disabled, the following code is mangled:

fn foo {
    let f = bar(); // comment for this line
    // some comment here to describe the next line
    let b = baz();
}

Which gets "corrected" to the following:

fn foo {
    let f = bar(); // comment for this line
                   // some comment here to describe the next line
    let b = baz();
}

Also,

fn foo {
    let f = bar(); // comment for this line
    // let b = baz();
}

Gets equally transformed to

fn foo {
    let f = bar(); // comment for this line
                   // let b = baz();
}

Note that I expect neither wrap_comments nor normalize_comments to do this.

Suggested fix: if the comment on the next line starts at index 0, do not try to align them.
See also #2949, which was fixed.