Avoid using an already freed string for content id
Avoid using an already freed string for content id

* src/modest-tny-msg.c (add_attachments): get a copy of old content id
  intead of a plain reference, as this may be freed before we use it
  for the new attachment.

community-ssu/modest,community-ssu/modest,community-ssu/modest,community-ssu/modest