Use taxonomy_get_term() to load the $vid in nodewords_load_tags()

In nodewords_load_tags() it checks to see if the $tags array is empty - if it is empty and the $type is a term it checks to see if there are any metatags assigned for the vocabulary. To get the vocabulary vid it runs db_result(db_query()). Most of the time this code executes and tries to load the vocabulary's data it will be on a term page, which has already loaded the term via taxonomy_get_term() and which then means it is cached. As a result, there should not be any extra queries executed and it should just get the vocabulary vid from taxonomy_get_term().