systemctl: dont's how memory limits that aren't available via D-Bus props

When using an old systemctl on a new PID 1 the "startup" memory limit
props are not initialized and currently be shown in status output as
zero, even though there's code to suppress the output in that case. Alas
it doesn't work, because the relevant fields are not marked as
"unset"... Fix that.

Follow-up for: 53fda560dc

src/systemctl/systemctl-show.c

@@ -2061,10 +2061,14 @@ static int show_one(
                 .runtime_max_sec = USEC_INFINITY,
                 .memory_current = UINT64_MAX,
                 .memory_high = CGROUP_LIMIT_MAX,
+                .startup_memory_high = CGROUP_LIMIT_MAX,
                 .memory_max = CGROUP_LIMIT_MAX,
+                .startup_memory_max = CGROUP_LIMIT_MAX,
                 .memory_swap_max = CGROUP_LIMIT_MAX,
+                .startup_memory_swap_max = CGROUP_LIMIT_MAX,
                 .memory_zswap_max = CGROUP_LIMIT_MAX,
-                .memory_limit = UINT64_MAX,
+                .startup_memory_zswap_max = CGROUP_LIMIT_MAX,
+                .memory_limit = CGROUP_LIMIT_MAX,
                 .memory_available = CGROUP_LIMIT_MAX,
                 .cpu_usage_nsec = UINT64_MAX,
                 .tasks_current = UINT64_MAX,