return empty list instead of None in case of error

git-svn-id: svn://svn.cy55.de/Zope3/src/loops/trunk@4133 fd906abe-77d9-0310-91a1-e0d9ade77398

integrator/office/base.py

@@ -87,7 +87,7 @@ class OfficeFile(ExternalFileAdapter):
         except IOError, e:
             from logging import getLogger
             self.logger.warn(e)
-            return
+            return []
         if self.propFileName not in zf.namelist():
             self.logger.warn('Custom properties not found in file %s.' %
                              self.externalAddress)