HPCC-9409 Protect access to delayed inputs with a critical section

The timings for the delayed inputs could be requested at the same
time that they were being changed, causing an access to an invalid
pointer.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4436 from ghalliday/issue9409

HPCC-9409 Protect access to delayed inputs with a critical sec

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>