fcl-db: sqldb: Some SQLConnections does not support statement [un]preparation, so let them do cleanup f.e. cancel pending queries and/or free resultset when dataset is closed.

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@24803 3ad0048d-3df7-0310-abae-a5850022a9f2