HPCC-8978 - Issues with SOAPCALL in child queries.

Fix crash caused when SOAPCALL used in child queries.
Make soapcall helper restartable.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Minor changes following review

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #4118 from jakesmith/hpcc-8978

HPCC-8978 - Issues with SOAPCALL in child queries.

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>