Comma-insertion in array can break syntax

coder-format doesn't like empty multi-line arrays like this:

  $item = array(
    'key' => array(
    ),
    'another' => 1,
  );

It will add an unwanted comma at the end of the second line, which is not valid syntax and produces a compile-time error.

Attached patch makes sure we're never inserting commas at the beginning of an array.