Mysql shouldn't segfault in database-query when running a command with no resultset.

From docs at http://dev.mysql.com/doc/refman/5.0/en/mysql-real-query.html and
http://dev.mysql.com/doc/refman/5.0/en/mysql-field-count.html after performing the query
and attempting to get a result set, the RS ptr should be checked for null and
if it is check mysql_errno to see if there actually was an error, or just no result.

This patch makes database-query return NIL if there was no resultset.