add else statement to define content_type variable

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@28951 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/File.py

@@ -169,6 +169,8 @@ class File(Document, CMFFile, ConversionCacheMixin):
       content_type,enc = mimetypes.guess_type(fname)
       if content_type is not None:
         self.setContentType(content_type)
+    else:
+      content_type = None
     return content_type
 
   security.declareProtected(Permissions.ModifyPortalContent,'PUT')