Initialize shared memory copy of ckptXidEpoch correctly when not in recovery.
Initialize shared memory copy of ckptXidEpoch correctly when not in recovery.

This bug was introduced by commit 20d98ab6e4110087d1816cd105a40fcc8ce0a307,
so backpatch this to 9.0-9.2 like that one.

This fixes bug #6710, reported by Tarvi Pillessaar

postmind-net/postgres-xl,kmjungersen/PostgresXL,snaga/postgres-xl,postmind-net/postgres-xl,kmjungersen/PostgresXL,snaga/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl,snaga/postgres-xl,kmjungersen/PostgresXL,snaga/postgres-xl,postmind-net/postgres-xl,postmind-net/postgres-xl,arcivanov/postgres-xl,snaga/postgres-xl,arcivanov/postgres-xl,kmjungersen/PostgresXL,kmjungersen/PostgresXL,arcivanov/postgres-xl,arcivanov/postgres-xl,postmind-net/postgres-xl