links--dropbutton does not display the first menu item

Problem/Motivation

When using a dropdown in the menu bar, the first link should be displayed as a button next to the dropdown menu, which displays the remaining links. This is being done both in menu.theme radix_preprocess_links__dropbutton() and in the links--dropbutton.html.twig template, resulting in the loss of the first item.

Steps to reproduce

1. Create a drop button. I created it in the menu bar, but I don't think that's relevant.
2. Display the page and notice that the button contains the second menu item.

Proposed resolution

Either the pre-process function should leave the button in the links, or the template should be modified to use the button variable and display all the links.