Searching using the custom search fails to restrict the results to the specific FAQ

To reproduce:

• Search for a term using the custom search UI. This will lead to a URL like http://localhost:8080/xwiki/bin/view/FAQ/FAQSearch?space=FAQ&wikinames=xwiki&text=test.
• Then on the search result page, search again by pressing the Search button.

You'll notice that it leads to a URL like http://localhost:8080/xwiki/bin/view/FAQ/FAQSearch?highlight=true&facet=true&r=&text=test&sort=score which loses the space query string parameter. Thus the search is done on the full wiki.