mimetypes.guess_extension fails if given parameter is None

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@23844 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5OOo/OOoTemplate.py

@@ -405,7 +405,8 @@ xmlns:config="http://openoffice.org/2001/config" office:version="1.0">
 
       actual_idx = self.document_counter.next()
       pic_name = 'Pictures/picture%d%s' \
-                 % (actual_idx, guess_extension(picture_type) or '')
+                 % (actual_idx,
+                    picture_type and guess_extension(picture_type) or '')
 
       # XXX: Pictures directory not managed (seems facultative)
       #  <manifest:file-entry manifest:media-type="" manifest:full-path="ObjBFE4F50D/Pictures/"/>