schedule sending when writing initial or handshake crypto data

No functional change expected. We already did schedule sending for all
cases but the ClientHello. Scheduling explicitly allows us to remove
this corner case.

connection.go

@@ -514,10 +514,6 @@ func (s *connection) run() error {
 		}
 	}()
 
-	if s.perspective == protocol.PerspectiveClient {
-		s.scheduleSending() // so the ClientHello actually gets sent
-	}
-
 	var sendQueueAvailable <-chan struct{}
 
 runLoop:
@@ -1406,8 +1402,10 @@ func (s *connection) handleHandshakeEvents() error {
 			err = s.dropEncryptionLevel(protocol.Encryption0RTT)
 		case handshake.EventWriteInitialData:
 			_, err = s.initialStream.Write(ev.Data)
+			s.scheduleSending()
 		case handshake.EventWriteHandshakeData:
 			_, err = s.handshakeStream.Write(ev.Data)
+			s.scheduleSending()
 		}
 		if err != nil {
 			return err

connection_test.go

@@ -2588,6 +2588,7 @@ var _ = Describe("Client Connection", func() {
 			defer GinkgoRecover()
 			cryptoSetup.EXPECT().StartHandshake().MaxTimes(1)
 			cryptoSetup.EXPECT().NextEvent().Return(handshake.Event{Kind: handshake.EventNoEvent})
+			conn.scheduleSending()
 			conn.run()
 		}()
 		Eventually(done).Should(BeClosed())