[leapp] Failed to read machine ID from container image: Invalid argument

Description of problem:
If the /etc/machine-id file is not well-formed, systemd-nspawn used by leapp exits with a -1 return code, leading to the emergency shell. This is harmless as it happens very early and the system is untouched.

Version-Release number of selected component (if applicable):
leapp-upgrade-el7toel8-0.17.0-1.el7_9

How reproducible:
Always

Steps to Reproduce:
1. echo >> /etc/machine-id
2. leapp upgrade

Actual results:
[ 2.462635] upgrade[691]: Failed to read machine ID from container image: Invalid argument
[ 2.476214] upgrade[690]: (sd-namespace) failed with exit status 1.

Expected results:
Possibly an inhibitor.

Additional info:

• Never observed such an issue, hence very low sev. This file should not have been touched (by a human or a script).
• Probably the same for IPU 8>9.
• The KCS I linked could be enough.
• Some systemd-nspawn excerpt:

systemd-239/src/nspawn/nspawn.c:
2187 static int setup_machine_id(const char *directory) {
:
2198
2199 etc_machine_id = prefix_roota(directory, "/etc/machine-id");
2200
2201 r = id128_read(etc_machine_id, ID128_PLAIN, &id);
2202 if (r < 0) {
2203 if (!IN_SET(r, -ENOENT, -ENOMEDIUM)) /* If the file is missing or empty, we don't mind */
2204 return log_error_errno(r, "Failed to read machine ID from container image: %m");

systemd-239/src/libsystemd/sd-id128/id128-util.c:
82 int id128_read_fd(int fd, Id128Format f, sd_id128_t *ret) {
:
102 case 33: /* plain UUID with trailing newline */
103 if (buffer[32] != '\n')
104 return -EINVAL;
105
106 fallthrough;
107 case 32: /* plain UUID without trailing newline */
108 if (f == ID128_UUID)
109 return -EINVAL;
110
111 buffer[32] = 0;
112 break;
113
114 case 37: /* RFC UUID with trailing newline */
115 if (buffer[36] != '\n')
116 return -EINVAL;
117
118 fallthrough;
119 case 36: /* RFC UUID without trailing newline */
120 if (f == ID128_PLAIN)
121 return -EINVAL;