Fix pg_recvlogical avoidance of superfluous Standby Status Update.

The defect suppressed a Standby Status Update message when bytes flushed
to disk had changed but bytes received had not changed.  If
pg_recvlogical then exited with no intervening Standby Status Update,
the next pg_recvlogical repeated already-flushed records.  The defect
could also cause superfluous messages, which are functionally harmless.
Back-patch to 9.5 (all supported versions).

Discussion: https://postgr.es/m/20200502221647.GA3941274@rfd.leadboat.com

Author: nmisch

src/bin/pg_basebackup/pg_recvlogical.c

@@ -126,7 +126,7 @@ sendFeedback(PGconn *conn, TimestampTz now, bool force, bool replyRequested)
 	 */
 	if (!force &&
 		last_written_lsn == output_written_lsn &&
-		last_fsync_lsn != output_fsync_lsn)
+		last_fsync_lsn == output_fsync_lsn)
 		return true;
 
 	if (verbose)