pgsql: Now that streaming replication switches between streaming mode

Log Message:
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Now that streaming replication switches between streaming mode and
restoring from archive, the last WAL segment is not necessarily open at
the end of recovery. Fix assertion that assumed that.

Fujii Masao, fixing the assertion failure reported by Martin Pihlak.

Modified Files:
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    pgsql/src/backend/access/transam:
        xlog.c (r1.369 -> r1.370)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlog.c?r1=1.369&r2=1.370)