Form error is thrown in luceneapi_query_parsed when no terms meet the minimum length and no element is defined

The luceneapi_query_parse() API function has an optional $element parameter that will set form errors attached to a form element. If the $element parameter is NULL, no form errors should be thrown. The fix for #711394: Search Lucene displays every item ignores search keyword has the side effect of throwing a form error in some instances even when $element is NULL.

This problem is exposed by the Search Lucene DidYouMean module because it has to parse the search query to get the passed terms. If no terms meet the minimum length requirement, a form error is thrown despite the fact that the $element parameter is NULL.