HPCC-12543 Create the deserializer object in the correct context

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6614 from ghalliday/issue12543

HPCC-12543 Create the deserializer object in the correct context

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>