protect access to tctable in up/downcontroller::cancel
protect access to tctable in up/downcontroller::cancel

- in case there was a logged out, there could be no table: we will
continue creating an empty committer

Acidburn0zzz/sdk,Acidburn0zzz/sdk,Acidburn0zzz/sdk,meganz/sdk,meganz/sdk,Acidburn0zzz/sdk,Acidburn0zzz/sdk,Acidburn0zzz/sdk,meganz/sdk,Acidburn0zzz/sdk,meganz/sdk,meganz/sdk,meganz/sdk,Acidburn0zzz/sdk,meganz/sdk