[trean] Import bookmarks without any category defined

[Chih-Wei Yeh]

Hi all:

  One of my user found that, if you haven't defined any category for your
trean bookmarks, importing bookmarks is possible, but the imported data
will not be displayed correctly. I noticed that it's impossible to add a
bookmark without any category defined. However, by the imported function,
it's possible for a new user to import his data without define a
category and fails. Could anyone help to resolve this problem by setting
up some restriction for the importing function? Or, for the best case, is
it possbile for users to import their bookmarks at top level without
errors?

  Thanks in advance.

Regards,
cwyeh