Update Extension.php

Avoid PHP warning.
Fix #151: Check for module status at /admin/reports/status
Fix #150: Hotfix: helper.real_path service should not include full system path for web assets
Fix #137: Throw exception if yaml_parse_file() can not parse data.
Merge branch 'dev-master' into views-improve

* dev-master:
  Fix #137: Throw exception if yaml_parse_file() can not parse data.
  Fix #150: Hotfix: helper.real_path service should not include full system path for web assets
  Fix #151: Check for module status at /admin/reports/status
  Update Extension.php