httprequests.lua: use proper binding to get current stream length
httprequests.lua: use proper binding to get current stream length

... instead of the "length" object variable.

Ref #17285

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc