Demuxer: emit an error in case of incomplete PES packet and EOF

At the moment, the demuxer returns (nil, nil) when there are no
more TS packets and a PES packet has not been fully received.
This patch makes the demuxer emit (nil, ErrNoMorePackets).

demuxer.go

@@ -119,14 +119,16 @@ func (dmx *Demuxer) NextData() (d *DemuxerData, err error) {
 					}
 
 					// Parse data
-					if ds, err = parseData(ps, dmx.optPacketsParser, dmx.programMap); err != nil {
+					var err2 error
+					if ds, err2 = parseData(ps, dmx.optPacketsParser, dmx.programMap); err2 != nil {
 						// We need to silence this error as there may be some incomplete data here
 						// We still want to try to parse all packets, in case final data is complete
 						continue
 					}
 
 					// Update data
 					if d = dmx.updateData(ds); d != nil {
+						err = nil
 						return
 					}
 				}

demuxer_test.go

@@ -101,6 +101,34 @@ func TestDemuxerNextData(t *testing.T) {
 	assert.EqualError(t, err, ErrNoMorePackets.Error())
 }
 
+func TestDemuxerNextDataInvalidFinalPackets(t *testing.T) {
+	buf := &bytes.Buffer{}
+	bufWriter := astikit.NewBitsWriter(astikit.BitsWriterOptions{Writer: buf})
+
+	// Packet that is part of an incomplete PES
+	b1, _ := packet(PacketHeader{
+		ContinuityCounter: uint8(0),
+		PID: 256,
+		PayloadUnitStartIndicator: true,
+		HasPayload: true,
+	}, PacketAdaptationField{}, []byte{0x01, 0x02, 0x03, 0x04}, true)
+	bufWriter.Write(b1)
+
+	// Packet that is part of an incomplete PES
+	b2, _ := packet(PacketHeader{
+		ContinuityCounter: uint8(1),
+		PID: 256,
+		HasPayload: true,
+	}, PacketAdaptationField{}, []byte{0x01, 0x02, 0x03, 0x04}, true)
+	bufWriter.Write(b2)
+
+	// The demuxer must return "no more packets"
+	dmx := NewDemuxer(context.Background(), bytes.NewReader(buf.Bytes()))
+	d, err := dmx.NextData()
+	assert.Equal(t, (*DemuxerData)(nil), d)
+	assert.EqualError(t, err, "astits: no more packets")
+}
+
 func TestDemuxerNextDataPATPMT(t *testing.T) {
 	pat := hexToBytes(`474000100000b00d0001c100000001f0002ab104b2ffffffffffffffff
 	ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff