HPCC-10262 Base Store cached data could "leak" between instances

Fetching two result sets at the same time can cause their results to get written to each other.

Fixes HPCC-10262

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #5031 from GordonSmith/HPCC-10262

HPCC-10262 Base Store cached data could "leak" between instances

Reviewed-By: Miguel Vazquez <miguel.vazquez@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>