unit: return a better error state for unit_get_unit_file_preset() if we have no fragment path

We'd previously return what was already set. Let's instead return a
clear ENOEXEC in this case, to make clear what is going on: preset logic
doesn't apply to units which lag a fragment path.

Author: poettering

src/core/unit.c

@@ -4173,12 +4173,12 @@ PresetAction unit_get_unit_file_preset(Unit *u) {
 
         assert(u);
 
-        if (u->unit_file_preset >= 0 || !u->fragment_path)
+        if (u->unit_file_preset >= 0)
                 return u->unit_file_preset;
 
         /* If this is a transient or perpetual unit file it doesn't make much sense to ask the preset
          * database about this, because enabling/disabling makes no sense for either. Hence don't. */
-        if (u->transient || u->perpetual)
+        if (!u->fragment_path || u->transient || u->perpetual)
                 return (u->unit_file_preset = -ENOEXEC);
 
         _cleanup_free_ char *bn = NULL;