silence exceptions in __del__ method

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@42367 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/patches/CMFCoreSkinnable.py

@@ -181,6 +181,8 @@ class SkinDataCleanup:
 
   def __del__(self):
     tid = self.tid
+    if SKINDATA is None:
+      return
     skindata = SKINDATA.get(tid)
     if skindata is not None:
       if self.hashSkinData(skindata) == self.skindata_id: