Implement a proper workaround for the broken seeking in VLC.
Implement a proper workaround for the broken seeking in VLC.

Only enable the workaround when the User-Agent reports VLC, not in any
other case to avoid messing up the code for non-broken clients.

winlinvip/feng,winlinvip/feng,lscube/feng,lscube/feng,lscube/feng,winlinvip/feng