fcl-db: base: for UniDirectional DataSet initialize  BufferCount=1; + adapt also test (checked with Delphi, where for UniDirectional sql dataset (f.e.TSQLTable) on Next is also generated deDataSetScroll:-1 not deDataSetScroll:0)

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25174 3ad0048d-3df7-0310-abae-a5850022a9f2