[core] replace ++ with incPos() in getTimespan_ms()
[core] replace ++ with incPos() in getTimespan_ms()

Cinegy/srt,Haivision/srt,ethouris/srt,ethouris/srt,Cinegy/srt,ethouris/srt,Haivision/srt,Cinegy/srt,Haivision/srt,ethouris/srt,Cinegy/srt,Haivision/srt