[ticket/11859] Make avatar drivers return template filename

The service name might not follow the expected naming scheme which would
cause abnormally long filenames and confusion for authors that might add
more avatar drivers.

PHPBB3-11859

phpBB/phpbb/avatar/driver/local.php

@@ -134,6 +134,14 @@ class local extends \phpbb\avatar\driver\driver
 		);
 	}
 
+	/**
+	* @inheritdoc
+	*/
+	public function get_template_name()
+	{
+		return 'ucp_avatar_options_local.html';
+	}
+
 	/**
 	* Get a list of avatars that are locally available
 	* Results get cached for 24 hours (86400 seconds)