[Janther]

Fixing a particular bug where a line comment in the middle of an empty list of parameters or arguments would trigger a wrong format.
As a bonus, I added the possibility to print a comment to an empty struct, which was throwing with a Comment not printed error.

// Original
function reserved(
    // parameters will be added later
) public {}

// prettier-plugin-solidity@2.4.1
function reserved(// parameters will be added later) public {}

// This PR
function reserved(
    // parameters will be added later
) public {}

I added the fixtures in the first commit so you can review the fixes by commit.