cfix: View: Replace assert by return
Fixes assertion error on switching chat, when FT db table contains items:
Traceback (most recent call last):
File "gajim/gtk/chat_page.py", line 134, in _on_chat_selected
self._chat_stack.show_chat(account, jid)
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
File "gajim/gtk/chat_stack.py", line 223, in show_chat
self._chat_control.switch_contact(self._current_contact)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
File "gajim/gtk/control.py", line 234, in switch_contact
self._request_history(None, True)
~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^
File "gajim/gtk/control.py", line 598, in _request_history
self._add_messages([row])
~~~~~~~~~~~~~~~~~~^^^^^^^
File "gajim/gtk/control.py", line 546, in _add_messages
self._add_db_row(msg)
~~~~~~~~~~~~~~~~^^^^^
File "gajim/gtk/control.py", line 535, in _add_db_row
self._scrolled_view.add_jingle_file_transfer(message=message)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
File "gajim/gtk/conversation/view.py", line 477, in add_jingle_file_transfer
assert isinstance(self._contact, BareContact)
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError