fcl-db: base: fix streaming of NULL values in FPCBinaryDatapacketReader (like in Delphi null bitmap is stored in the beginning of record and null values are not stored in row data) + tests


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25524 3ad0048d-3df7-0310-abae-a5850022a9f2