HPCC-10072 - Avoid roxiemem allocator cache deadlock

ensure() calling createAllocator could cause other threads
to deadlock on cache calls.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #4865 from jakesmith/hpcc-10072

HPCC-10072 - Avoid roxiemem allocator cache deadlock

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>