Do not show dialog of print labels if the Parameter is not configured

This modified just show yeno window if the label path parameter
is diferent of None.

Fixes: http://bugs.async.com.br/show_bug.cgi?id=5545

Change-Id: I06496236ad5de2c623a6ef8b8f8aa07219420255
Merge "Do not show dialog of print labels if the Parameter is not configured"