HPCC-11765 Avoid compiler warning for potentially uninitialized

I don't think this could have bitten us, it would imply that
getRowStream/getKeyStream had been recalled, which it should not
be.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #6171 from jakesmith/hpcc-11765

HPCC-11765 Avoid compiler warning for potentially uninitialized

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>