SeqNo bug, increment needed only when chunk removed

[hori-ryota]

m3u8/writer.go at master · grafov/m3u8

Here is necessary code.

It cause following bug,

• first

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-TARGETDURATION:12
#EXTINF:10.000,
0ts

• next

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:1
#EXT-X-TARGETDURATION:12
#EXTINF:10.000,
0ts
#EXTINF:10.000,
1ts

• correct

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-TARGETDURATION:12
#EXTINF:10.000,
0ts
#EXTINF:10.000,
1ts

[Alexander I.Grafov]

Hmm... did we fix it? :|