pgsql: Use ereport(ERROR) instead of Assert() to emit syncrep_parser er

Use ereport(ERROR) instead of Assert() to emit syncrep_parser error.

The existing code would either Assert or generate an invalid
SyncRepConfig variable, neither of which is desirable. A regular
error should be thrown instead.

This commit silences compiler warning in non assertion-enabled builds.

Per report from Jeff Janes.
Suggested fix by Tom Lane.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/0038c1e2181b520a9307aae6587e110468072392

Modified Files
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src/backend/replication/syncrep.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)