Livetv chain

Hi Christian,

Here two commits:

- About program break: Adding code to retry chain update for a last chance (Nachteule case). This code has no impact when backend returns new chain as required and at time.

- LiveTV chain seek: Finally i resolved the issue. First the function didn't returned the absolute offset in the chain after seeking but the offset in the current file ! Second the SEEK_CUR part was wrong because when switching to an other file, the offset was relative to the current read position ! So i force SEEK_SET with new position in the new file. Now all seems good. Rewind and forward work great.