pg_upgrade: fix off-by-one mistake in snprintf

snprintf counts trailing NUL towards the char limit.  Failing to account
for that was causing an invalid value to be passed to pg_resetxlog -l,
aborting the upgrade process.

contrib/pg_upgrade/controldata.c

@@ -425,7 +425,7 @@ get_control_data(ClusterInfo *cluster, bool live_check)
 	{
 		if (got_log_id && got_log_seg)
 		{
-			snprintf(cluster->controldata.nextxlogfile, 24, "%08X%08X%08X",
+			snprintf(cluster->controldata.nextxlogfile, 25, "%08X%08X%08X",
 					 tli, logid, segno);
 			got_nextxlogfile = true;
 		}