HPCC-8889 getEnv cores on roxie when no packages are defined

Regression in 3.10.4 caused by:
https://github.com/hpcc-systems/HPCC-Platform/pull/3995

Signed-off-by: Anthony Fishbeck <Anthony.Fishbeck@lexisnexis.com>
Merge pull request #4029 from afishbeck/getEnvCoreNoPackages8889

HPCC-8889 getEnv cores on roxie when no packages are defined

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>