Setup: fix DM channel startup state
Setup: fix DM channel startup state

I broke this on a previous commit. The state should only be
ChanLoadPending if we have a pending scrollback fetch; we don't fetch
scrollback for DM channels, but we *do* fetch channel metadata. I
mistakenly thought that meant we wanted them set to ChanLoadPending.

aisamanra/matterhorn,matterhorn-chat/matterhorn