hack-ign-3to2: Don't crash if no storage section is defined
I hit this in a config that only writes `systemd` units.
@@ -29,7 +29,7 @@ if vmajor == 2:
elif vmajor != 3:
raise SystemExit(f"Unsupported version {v}")
ign['ignition']['version'] = '2.2.0'
-for f in ign['storage'].get('files', []):
+for f in ign.get('storage', {}).get('files', []):
f['filesystem'] = "root"
append = f.get('append')
if append is not None:
