tree: Fix potential NULL pointer dereference in nvme_host_get_ids()

The nvme_host_get_hostid() and nvme_host_get_hostnqn() functions can
return NULL when the host configuration is incomplete or invalid. Using
strdup() directly on these return values causes a segmentation fault
when NULL is passed to strdup().

Replace strdup() calls with xstrdup() to safely handle NULL input
values.

Signed-off-by: Stephen Cheng <stephen.cheng@citrix.com>

Author: Stephen Cheng

src/nvme/tree.c

@@ -145,9 +145,9 @@ int nvme_host_get_ids(nvme_root_t r,
 	h = nvme_first_host(r);
 	if (h) {
 		if (!hid)
-			hid = strdup(nvme_host_get_hostid(h));
+			hid = xstrdup(nvme_host_get_hostid(h));
 		if (!hnqn)
-			hnqn = strdup(nvme_host_get_hostnqn(h));
+			hnqn = xstrdup(nvme_host_get_hostnqn(h));
 	}
 
 	/* /etc/nvme/hostid and/or /etc/nvme/hostnqn */