[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/upload.php

@@ -167,6 +167,14 @@ class upload extends \phpbb\avatar\driver\driver
 		return true;
 	}
 
+	/**
+	* @inheritdoc
+	*/
+	public function get_template_name()
+	{
+		return 'ucp_avatar_options_upload.html';
+	}
+
 	/**
 	* Check if user is able to upload an avatar
 	*