pgsql: Initialize shared memory copy of ckptXidEpoch correctly when not

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

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/b6fe2dfda004e28f806c2424fff13063f8532d68

Modified Files
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src/backend/access/transam/xlog.c |    7 +++----
1 files changed, 3 insertions(+), 4 deletions(-)