Fix H264Writer writing 0 length payloads

Before we would call Write even if no bytes were available.

pkg/media/h264writer/h264writer.go

@@ -62,7 +62,7 @@ func (h *H264Writer) WriteRTP(packet *rtp.Packet) error {
 	}
 
 	data, err := h.cachedPacket.Unmarshal(packet.Payload)
-	if err != nil {
+	if err != nil || len(data) == 0 {
 		return err
 	}
 

pkg/media/h264writer/h264writer_test.go

@@ -153,3 +153,40 @@ func TestWriteRTP(t *testing.T) {
 		})
 	}
 }
+
+type writerCounter struct {
+	writeCount int
+}
+
+func (w *writerCounter) Write([]byte) (int, error) {
+	w.writeCount++
+
+	return 0, nil
+}
+
+func (w *writerCounter) Close() error {
+	return nil
+}
+
+func TestNoZeroWrite(t *testing.T) {
+	payloads := [][]byte{
+		{0x1c, 0x80, 0x01, 0x02, 0x03},
+		{0x1c, 0x00, 0x04, 0x05, 0x06},
+		{0x1c, 0x00, 0x07, 0x08, 0x09},
+		{0x1c, 0x00, 0x10, 0x11, 0x12},
+		{0x1c, 0x40, 0x13, 0x14, 0x15},
+	}
+
+	writer := &writerCounter{}
+	h264Writer := &H264Writer{
+		hasKeyFrame: true,
+		writer:      writer,
+	}
+
+	for i := range payloads {
+		assert.NoError(t, h264Writer.WriteRTP(&rtp.Packet{
+			Payload: payloads[i],
+		}))
+	}
+	assert.Equal(t, 1, writer.writeCount)
+}