fcl-db: bufdataset: TBufDataset autoincrement fields (ftAutoInc) are not restarted when dataset is closed and again reopened. See bug #25628

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@26622 3ad0048d-3df7-0310-abae-a5850022a9f2