plugins/inventory/lxd.py: fix listing of containers without os / release (#4351)

* plugins/inventory/lxd.py: fix listing of containers without os / release

In some cases, a container might be present, that was initialized empty, therefore lacking meta information about the os or the release.
Test if the data entry is None to avoid calling lower on it.

* Update plugins/inventory/lxd.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* Update plugins/inventory/lxd.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* Create 4351-inventory-lxd-handling_metadata_wo_os_and_release.yml

* fix yaml readability of changelog fragment

* Update changelogs/fragments/4351-inventory-lxd-handling_metadata_wo_os_and_release.yml

Co-authored-by: Felix Fontein <felix@fontein.de>

Co-authored-by: Felix Fontein <felix@fontein.de>
Co-authored-by: Malte Kuhn <mkuhn@maxcluster.de>

changelogs/fragments/4351-inventory-lxd-handling_metadata_wo_os_and_release.yml

@@ -0,0 +1,4 @@
+bugfixes:
+  - |
+    lxd inventory plugin - do not crash if OS and release metadata are not present
+    (https://github.com/ansible-collections/community.general/pull/4351).

plugins/inventory/lxd.py

@@ -666,9 +666,13 @@ class InventoryModule(BaseInventoryPlugin):
             # add network informations
             self.build_inventory_network(instance_name)
             # add os
-            self.inventory.set_variable(instance_name, 'ansible_lxd_os', self._get_data_entry('inventory/{0}/os'.format(instance_name)).lower())
+            v = self._get_data_entry('inventory/{0}/os'.format(instance_name))
+            if v:
+                self.inventory.set_variable(instance_name, 'ansible_lxd_os', v.lower())
             # add release
-            self.inventory.set_variable(instance_name, 'ansible_lxd_release', self._get_data_entry('inventory/{0}/release'.format(instance_name)).lower())
+            v = self._get_data_entry('inventory/{0}/release'.format(instance_name))
+            if v:
+                self.inventory.set_variable(instance_name, 'ansible_lxd_release', v.lower())
             # add profile
             self.inventory.set_variable(instance_name, 'ansible_lxd_profile', self._get_data_entry('inventory/{0}/profile'.format(instance_name)))
             # add state