avformat/hlsenc: refine EXT-X-BYTERANGE support for segments

avformat/hlsenc: refine EXT-X-BYTERANGE support for segments

refine EXT-X-BYTERANGE tag,
the spec link:
https://tools.ietf.org/html/draft-pantos-http-live-streaming-19#section-4.3.2.2
the apple doc:
https://developer.apple.com/library/ios/technotes/tn2288/_index.html#
//apple_ref/doc/uid/DTS40012238-CH1-BYTE_RANGE_SUPPORT_FOR_SEGMENTS

command line:
./ffmpeg -i ~/Movies/objectC/a.mp4 -c copy -f hls -hls_time 7
 -hls_list_size 0 -hls_segment_size 2500000 -t 40 output-test.m3u8
output:
localhost:ffmpeg liuqi$ ll *.ts ;cat output-test.m3u8
 -rw-r--r--  1 liuqi  staff  2792176  9 12 14:44 output-test0.ts
 -rw-r--r--  1 liuqi  staff  3112528  9 12 14:44 output-test3.ts
 -rw-r--r--  1 liuqi  staff  3377420  9 12 14:44 output-test6.ts
 -rw-r--r--  1 liuqi  staff  1228016  9 12 14:44 output-test7.ts
 #EXTM3U
 #EXT-X-VERSION:4
 #EXT-X-TARGETDURATION:10
 #EXT-X-MEDIA-SEQUENCE:0
 #EXTINF:9.021000,
 #EXT-X-BYTERANGE:1334988@0
 output-test0.ts
 #EXTINF:3.000000,
 #EXT-X-BYTERANGE:721356@1334988
 output-test0.ts
 #EXTINF:3.000000,
 #EXT-X-BYTERANGE:735832@2056344
 output-test0.ts
 #EXTINF:6.000000,
 #EXT-X-BYTERANGE:1645940@0
 output-test3.ts
 #EXTINF:3.000000,
 #EXT-X-BYTERANGE:715152@1645940
 output-test3.ts
 #EXTINF:3.000000,
 #EXT-X-BYTERANGE:751436@2361092
 output-test3.ts
 #EXTINF:9.000000,
 #EXT-X-BYTERANGE:3377420@0
 output-test6.ts
 #EXTINF:3.960000,
 #EXT-X-BYTERANGE:1228016@0
 output-test7.ts
 #EXT-X-ENDLIST
 localhost:ffmpeg liuqi$

 ticket-id: #5839

Signed-off-by: Steven Liu <lingjiujianke@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>