portable: remove drop-in configs even if the main unit file does not exist

When we run `portablectl detach --enable --runtime`, then it triggers
`DisableUnitFilesWithFlags` DBus method and the main unit file is
removed, but its drop-ins are not. Hence, portable_detach() failed to
list existing portable units.

This makes the loop for listing portable units also accept drop-in
directories. So, all remaining drop-in directories are correctly
removed.

Before:
```
testsuite-29.sh[600]: + portablectl detach --now --runtime --enable /tmp/rootdir minimal-app0
portablectl[1391]: (Matching unit files with prefixes 'minimal-app0'.)
portablectl[1391]: Queued /org/freedesktop/systemd1/job/1812 to call StopUnit on portable service minimal-app0-foo.service.
portablectl[1391]: Removed "/run/systemd/system.attached/minimal-app0-foo.service".
portablectl[1391]: Queued /org/freedesktop/systemd1/job/1813 to call StopUnit on portable service minimal-app0.service.
portablectl[1391]: Removed "/run/systemd/system.attached/minimal-app0.service".
portablectl[1391]: Got result done/Success for job minimal-app0-foo.service
portablectl[1391]: Got result done/Success for job minimal-app0.service
portablectl[1391]: DetachImage failed: No unit files associated with '/tmp/rootdir' found attached to the system. Image not attached?
```

After:
```
testsuite-29.sh[508]: + portablectl detach --now --runtime --enable /tmp/rootdir minimal-app0
portablectl[1076]: (Matching unit files with prefixes 'minimal-app0'.)
portablectl[1076]: Queued /org/freedesktop/systemd1/job/1946 to call StopUnit on portable service minimal-app0-foo.service.
portablectl[1076]: Removed "/run/systemd/system.attached/minimal-app0-foo.service".
portablectl[1076]: Queued /org/freedesktop/systemd1/job/1947 to call StopUnit on portable service minimal-app0.service.
portablectl[1076]: Removed "/run/systemd/system.attached/minimal-app0.service".
portablectl[1076]: Removed /run/systemd/system.attached/minimal-app0.service.d/10-profile.conf.
portablectl[1076]: Removed /run/systemd/system.attached/minimal-app0.service.d/20-portable.conf.
portablectl[1076]: Removed /run/systemd/system.attached/minimal-app0.service.d.
portablectl[1076]: Removed /run/systemd/system.attached/minimal-app0-foo.service.d/10-profile.conf.
portablectl[1076]: Removed /run/systemd/system.attached/minimal-app0-foo.service.d/20-portable.conf.
portablectl[1076]: Removed /run/systemd/system.attached/minimal-app0-foo.service.d.
portablectl[1076]: Removed /run/portables/rootdir.
portablectl[1076]: Removed /run/systemd/system.attached.
```

1 files changed, 23 insertions, 9 deletions

diff --git a/src/portable/portable.c b/src/portable/portable.c
index 254d9f6abe..a8536c6692 100644
--- a/src/portable/portable.c
+++ b/src/portable/portable.c
@@ -1559,33 +1559,47 @@ int portable_detach(
         }
 
         FOREACH_DIRENT(de, d, return log_debug_errno(errno, "Failed to enumerate '%s' directory: %m", where)) {
-                _cleanup_free_ char *marker = NULL;
+                _cleanup_free_ char *marker = NULL, *unit_name = NULL;
+                const char *dot;
+
+                /* When a portable service is enabled with "portablectl --runtime attach", and is disabled
+                 * with "portablectl --enable detach", which calls DisableUnitFilesWithFlags DBus method,
+                 * the main unit file is removed, but its drop-ins are not. Hence, here we need to list both
+                 * main unit files and drop-in directories (without the main unit files). */
+
+                dot = endswith(de->d_name, ".d");
+                if (dot)
+                        unit_name = strndup(de->d_name, dot - de->d_name);
+                else
+                        unit_name = strdup(de->d_name);
+                if (!unit_name)
+                        return -ENOMEM;
 
-                if (!unit_name_is_valid(de->d_name, UNIT_NAME_ANY))
+                if (!unit_name_is_valid(unit_name, UNIT_NAME_ANY))
                         continue;
 
                 /* Filter out duplicates */
-                if (set_contains(unit_files, de->d_name))
+                if (set_contains(unit_files, unit_name))
                         continue;
 
-                if (!IN_SET(de->d_type, DT_LNK, DT_REG))
+                if (dot ? !IN_SET(de->d_type, DT_LNK, DT_DIR) : !IN_SET(de->d_type, DT_LNK, DT_REG))
                         continue;
 
-                r = test_chroot_dropin(d, where, de->d_name, name_or_path, extension_image_paths, &marker);
+                r = test_chroot_dropin(d, where, unit_name, name_or_path, extension_image_paths, &marker);
                 if (r < 0)
                         return r;
                 if (r == 0)
                         continue;
 
-                r = unit_file_is_active(bus, de->d_name, error);
+                r = unit_file_is_active(bus, unit_name, error);
                 if (r < 0)
                         return r;
                 if (!FLAGS_SET(flags, PORTABLE_REATTACH) && r > 0)
-                        return sd_bus_error_setf(error, BUS_ERROR_UNIT_EXISTS, "Unit file '%s' is active, can't detach.", de->d_name);
+                        return sd_bus_error_setf(error, BUS_ERROR_UNIT_EXISTS, "Unit file '%s' is active, can't detach.", unit_name);
 
-                r = set_put_strdup(&unit_files, de->d_name);
+                r = set_ensure_consume(&unit_files, &string_hash_ops_free, TAKE_PTR(unit_name));
                 if (r < 0)
-                        return log_debug_errno(r, "Failed to add unit name '%s' to set: %m", de->d_name);
+                        return log_oom_debug();
 
                 for (const char *p = marker;;) {
                         _cleanup_free_ char *image = NULL;