The search bar takes too much width when folded

How to reproduce:

• Edit the page XWiki.Alerts.Code.AlertsMenuUIX with the object editor
• Inside the XWiki.UIExtensionClass, replace order=20000 by order=40000.
• Save the page
• Look at the top bar.

Expected state:

• The alert button should be placed immediately at the left of the search button

Actual state:

• There is a gap between the alert button and the search button, corresponding to the width of the search bar when it is displayed.

After a quick investigation, I think this is because the width of the text field was set to 0 in the past, but it has been changed with XWIKI-20733.