HPCC-12010 Fix deadlock in onActivity cache building

If building, whilst a queue request is processing, e.g.
onSetJobPriority, the two threads involved can deadlock each
other.
Regression introduced by HPCC-11637

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
HPCC-12010 Additional changes following review

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #6298 from jakesmith/hpcc-12010

HPCC-12010 Fix deadlock in onActivity cache building

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>
Community Edition 4.2.6-3 Gold

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge branch 'candidate-4.2.6' into candidate-5.0.0

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>

Conflicts:
	esp/services/ws_smc/ws_smcService.cpp
Community Edition 5.0.0-3 Gold

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>