Guess encoding if the provided one does not exist.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@26498 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/EmailDocument.py

@@ -137,7 +137,7 @@ class EmailDocument(File, TextDocument):
             text = text.decode(encoding).encode('utf-8')
           else:
             text = text.decode().encode('utf-8')
-        except UnicodeDecodeError:
+        except (UnicodeDecodeError, LookupError), error_message:
           encoding = self._guessEncoding(text)
           if encoding is not None:
             text = text.decode(encoding).encode('utf-8')