Initialize ListenSocket array earlier.

After commit b0bea38705, syslogger prints 63 warnings about failing to
close a listen socket at postmaster startup. That's because the
syslogger process forks before the ListenSockets array is initialized,
so ClosePostmasterPorts() calls "close(0)" 64 times. The first call
succeeds, because fd 0 is stdin.

This has been like this since commit 9a86f03b4e in version 13, which
moved the SysLogger_Start() call to before initializing ListenSockets.
We just didn't notice until commit b0bea38705 added the LOG message.

Reported by Michael Paquier and Jeff Janes.

Author: Michael Paquier
Discussion: https://www.postgresql.org/message-id/ZOvvuQe0rdj2slA9%40paquier.xyz
Discussion: https://www.postgresql.org/message-id/ZO0fgDwVw2SUJiZx@paquier.xyz#482670177eb4eaf4c9f03c1eed963e5f
Backpatch-through: 13

src/backend/postmaster/postmaster.c

@@ -1143,6 +1143,17 @@ PostmasterMain(int argc, char *argv[])
 				 errmsg("could not remove file \"%s\": %m",
 						LOG_METAINFO_DATAFILE)));
 
+	/*
+	 * Initialize input sockets.
+	 *
+	 * Mark them all closed, and set up an on_proc_exit function that's
+	 * charged with closing the sockets again at postmaster shutdown.
+	 */
+	for (i = 0; i < MAXLISTEN; i++)
+		ListenSocket[i] = PGINVALID_SOCKET;
+
+	on_proc_exit(CloseServerPorts, 0);
+
 	/*
 	 * If enabled, start up syslogger collection subprocess
 	 */
@@ -1177,15 +1188,7 @@ PostmasterMain(int argc, char *argv[])
 
 	/*
 	 * Establish input sockets.
-	 *
-	 * First, mark them all closed, and set up an on_proc_exit function that's
-	 * charged with closing the sockets again at postmaster shutdown.
 	 */
-	for (i = 0; i < MAXLISTEN; i++)
-		ListenSocket[i] = PGINVALID_SOCKET;
-
-	on_proc_exit(CloseServerPorts, 0);
-
 	if (ListenAddresses)
 	{
 		char	   *rawstring;