fix(f3): handle a case where we might receive no manifest

In _theory_ a lotus node can return no manifest from `F3Manifest`. I
don't think that happens in practice but we should handle the case and
start over at the top (try to get another lease). If we really have no
manifest, lotus will tell us that F3 isn't ready yet and we'll backoff
for a bit.

node/modules/storageminer.go

@@ -491,7 +491,11 @@ func (p *f3Participator) awaitLeaseExpiry(ctx context.Context, lease api.F3Parti
 			}
 			log.Errorw("Failed to check F3 progress while awaiting lease expiry. Retrying after backoff.", "attempts", p.backoff.Attempt(), "backoff", p.backoff.Duration(), "err", err)
 			p.backOff(ctx)
-		case manifest.NetworkName != lease.Network:
+		case manifest == nil || manifest.NetworkName != lease.Network:
+			// If we got an unexpected manifest, or no manifest, go back to the
+			// beginning and try to get another ticket. Switching from having a manifest
+			// to having no manifest can theoretically happen if the lotus node reboots
+			// and has no static manifest.
 			return nil
 		}
 		switch progress, err := p.node.F3GetProgress(ctx); {