tree-wide: introduce strerror_safe()

src/journal/journalctl.c

@@ -1425,7 +1425,7 @@ static int add_boot(sd_journal *j) {
         r = get_boots(j, NULL, &boot_id, arg_boot_offset);
         assert(r <= 1);
         if (r <= 0) {
-                const char *reason = (r == 0) ? "No such boot ID in journal" : strerror(-r);
+                const char *reason = (r == 0) ? "No such boot ID in journal" : strerror_safe(r);
 
                 if (sd_id128_is_null(arg_boot_id))
                         log_error("Data from the specified boot (%+i) is not available: %s",

src/journal/journald-server.c

@@ -1061,7 +1061,7 @@ void server_driver_message(Server *s, pid_t object_pid, const char *message_id,
                 /* We failed to format the message. Emit a warning instead. */
                 char buf[LINE_MAX];
 
-                xsprintf(buf, "MESSAGE=Entry printing failed: %s", strerror(-r));
+                xsprintf(buf, "MESSAGE=Entry printing failed: %s", strerror_safe(r));
 
                 n = 3;
                 iovec[n++] = IOVEC_MAKE_STRING("PRIORITY=4");