fix(dropdown): insert clearable at correct dom position

[lubber-de]

Description

This PR makes sure a clearable icon is always positioned at the correct DOM node in case incomplete markup exists.

Testcase

The dropdown is instantiated twice.

• The first time, clearable should not be set, but the search input is missing in the markup, so FUI created the search input
• The second time, the dropdown should be clearable, but this time the search input is already existing. This results into the remove icon not being a direct sibling of the dropdown icon which in turn makes clearing selections not working anymore

Broken

Selected items are not clearable
https://jsfiddle.net/lubber/oktecuv2/8/

Fixed

Selected items are clearable
https://jsfiddle.net/lubber/oktecuv2/10/

Fixes

#2791

[mvorisek]

Bravo @lubber-de for finding the root of the problem, I tested this fix and it works.

[ko2in]

LGTM.