Argument name comment gets boken if there's another comment before.

[emilio]

Running rustfmt on the following Rust code:

fn foo() {
    bar(
        one_argument,
        another,
        and_another,
        // One comment explaining something below.
        /* argument_name = */ None,
    )
}

Generates the following diff:

         another,
         and_another,
         // One comment explaining something below.
-        /* argument_name = */ None,
+        /* argument_name = */
+        None,
     )
 }

However removing the single-line comment works as expected, which is inconsistent.