Update ZAbstractDataset.pas

Author: NickNevzorov

src/component/ZAbstractDataset.pas

@@ -913,7 +913,6 @@ function TZAbstractRWDataSet.PSUpdateRecord(UpdateKind: TUpdateKind;
             try
               DestStream := DestDataset.CreateBlobStream(DestField, bmWrite);
               try
-                DestStream.Size := 0;
                 DestStream.CopyFrom(SrcStream, 0);
               finally
                 DestStream.Free;