[Plugin: Plugin Last Updated] Doesn't remember non-repo plugins

For plugins, that are not hosted in official repository, check is always being made on every list load. This gets slooooooooow.

Quick dirty fix:

$response = unserialize( wp_remote_retrieve_body( $request ) );

if( empty( $response ) )
	return 'N/A';

https://www.ads-software.com/extend/plugins/plugin-last-updated/