systemctl: fix silent failure when --root is not found

Some calls to lookup_path_init() were not followed by any log emission.
E.g.:
$ SYSTEMD_LOG_LEVEL=debug systemctl --root=/missing enable unit; echo $?
1

Let's add a helper function and use it in various places.

$ SYSTEMD_LOG_LEVEL=debug build/systemctl --root=/missing enable unit; echo $?
Failed to initialize unit search paths for root directory /missing: No such file or directory
1
$ SYSTEMCTL_SKIP_SYSV=1 build/systemctl --root=/missing enable unit; echo $?
Failed to initialize unit search paths for root directory /missing: No such file or directory
Failed to enable: No such file or directory.
1

The repeated error in the second case is not very nice, but this is a niche
case and I don't think it's worth the trouble to trying to avoid it.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/shared/condition.c b/src/shared/condition.c
index 0a4072c9be..15b22a4006 100644
--- a/src/shared/condition.c
+++ b/src/shared/condition.c
@@ -785,7 +785,8 @@ static int condition_test_needs_update(Condition *c, char **env) {
         if (r < 0) {
                 log_debug_errno(r, "Failed to parse timestamp file '%s', using mtime: %m", p);
                 return true;
-        } else if (r == 0) {
+        }
+        if (isempty(timestamp_str)) {
                 log_debug("No data in timestamp file '%s', using mtime.", p);
                 return true;
         }