[ticket/10945] Display search query when search fails in native search

If search fails and common words are present, split_keywords returns false
and search.php file prints appropriate message of common words.
If search fails and there are no common words, split_keywords returns true
and keyword_search returns false so that the search query is displayed in
search box.

PHPBB3-10945

Conflicts:
	phpBB/phpbb/search/fulltext_native.php