marsadm: fix annoying perl warning

userspace/marsadm

@@ -2251,7 +2251,7 @@ sub primary_phase0 {
     check_todo($cmd, $res, "replay", 1, 0);
     # check that no logfile replay errors exist.
     my $replay_error = get_link("$mars/resource-$res/actual-$host/replay-code", 2);
-    if (int($replay_error) < 0) {
+    if (defined($replay_error) && $replay_error ne "" && int($replay_error) < 0) {
       lwarn "Logfile replay / recovery stopped with error code $replay_error.\n";
       ldie "Won't switch to avoid unnoticed data loss. You may however do a 'primary --force'.\n" unless $force;
     }