Improper usage of add_action to update plugin action links #646

Bug Description

This bug was spotted while doing static test for issue #622.

add_action( 'plugin_action_links_' . plugin_basename( PERFLAB_MAIN_FILE ), 'perflab_plugin_action_links_add_settings' );
used within function perflab_add_modules_page() inside admin/load.php ( line ), calls perflab_plugin_action_links_add_settings which only add a new link to existing links.

The code currently works because of the usage of array_unshift which updates reference array.

Steps to reproduce

1. Go to 'admin/load.php'
2. Scroll down to 'function perflab_add_modules_page()'
3. See error in the add_action( 'plugin_action_links_...

Screenshots

Additional Context

• PHP Version:
• OS: [e.g. iOS]
• Browser: [e.g. chrome, safari]
• Plugin Version: [e.g. 22]
• Device: [e.g. iPhone6]