Reset lastEffect when resuming SuspenseList (#18412)

We store an effect pointer so we can backtrack in the effect list in some
cases. This is a stateful variable. If we interrupt a render we need to
reset it.

This field was added after the optimization was added and I didn't remember
to reset it here.

Otherwise we end up not resetting the firstEffect so it points to a stale
list. As a result children don't end up inserted like we think they were.
Then we try to remove them it errors.

It would be nicer to just get rid of the effect list and use the tree for
effects instead. Maybe we still need something for deletions tho.