fcl-db: base: move method GetNewBlobBuffer from public to protected section as it was before rev.21735
For usage in TDataPacketReader descendants use RestoreBlobField method.

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25543 3ad0048d-3df7-0310-abae-a5850022a9f2