fcl-db: bufdataset: when index is added set IndexDefs.Updated to false to signal, that FIndexDefs and FIndexes are not synchronized. This allow next call to IndexDefs.Update (which tests Updated) do synchronization.

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@23723 3ad0048d-3df7-0310-abae-a5850022a9f2