Do not traceback if the server does not oprived options for list fields
get_tab_by_name() should specify a tab type whenever possible

For example, a tab can be named muc.example.com, if you do /list
muc.example.com.  If you then do /join muc.example.com, the error handler
needs to get the correct tab (the MucTab, not the MucListTab previously
opened).
This commit fixes the above issue (a traceback), and maybe some others like
that.
fix a tb in the otr plugin