peer+server: wait until peer is active to begin channel opening process

Without waiting, we would proceed to retrieve the remote peer's
supported features, which may have not been set due to not yet receiving
their Init message.

server.go

@@ -3207,6 +3207,18 @@ func (s *server) OpenChannel(
 	}
 	s.mu.RUnlock()
 
+	// We'll wait until the peer is active before beginning the channel
+	// opening process.
+	select {
+	case <-peer.activeSignal:
+	case <-peer.quit:
+		req.err <- fmt.Errorf("peer %x disconnected", pubKeyBytes)
+		return req.updates, req.err
+	case <-s.quit:
+		req.err <- ErrServerShuttingDown
+		return req.updates, req.err
+	}
+
 	// If the fee rate wasn't specified, then we'll use a default
 	// confirmation target.
 	if req.fundingFeePerKw == 0 {