Tab Horizontal Slider Fix

[Mil4n0r]

Checklist

• [x] Build process is done without errors. All tests pass in the /lib directory.
• [x] Self-reviewed the code before submitting.
• [x] Meets accessibility standards.
• [x] Added/updated documentation to /website as needed.
• [x] Added/updated tests as needed.

Description There was a problem firing the load event and the scroll arrows would only display inside Tabs when resizing the window.

It is now solved thanks to changing the way that the first load is handled.

Closes #1681