calgetshowpartitions fails if MDB started before MCS

See working_tpch1_comparelogonly/misc/calshowpartitions.sql

If Server is running and columnstore is started, the calgetshowpartitions uses an out of date shared memory segment for extent map. It may get the wrong answer or will throw a generic error if the requested shm segment doesn't exist.
The fix is to refresh the shm pointers before running the function.