largefiles: don't crash when cloning to a remote repo
The immediate crash was when checking for requirements immediately after this,
but lfcommands.downloadlfiles() will also crash if --all-largefiles is
specified. That has been in place since atleast
5884812686f7 (2.3-rc) without
anyone noticing.
I can't tell from the peer classes if there's a way to make the custom largefile
functionality work in this case, but atleast it doesn't crash.