Fix: Sphinx extension on Python3
Fix: Sphinx extension on Python3

This patch is fixing the WSME Sphinx extension to work with Python 3.
The patch just checks the return value from the find_service_path()
method before it tries to do anything with it.

Change-Id: I5a4cfa42a8768ce35a1c1a999431e842c7dde020
Closes-Bug: #1657435

stackforge/wsme