[FIX] base_geolocalize: geocode errors out on empty address

It's unclear whether that's a recent change or a long-standing issue,
however currently if geocode is called with an empty address string it
will reply with a 400 Bad Request, which gets raised as an exception and
forwarded to the user. That is not a great experience.

Shortcut the entire thing and just return None (= geolocation failed /
no geolocation) on trying to geolocate an empty address.

OPW-746686

backport of 74a89bcf5c

addons/base_geolocalize/models/res_partner.py

@@ -31,6 +31,8 @@ from openerp.tools.translate import _
 
 
 def geo_find(addr):
+    if not addr:
+        return None
     url = 'https://maps.googleapis.com/maps/api/geocode/json?sensor=false&address='
     url += urllib2.quote(addr.encode('utf8'))