fixed a refiller issue, which I think is triggered by H.264+Bframes (Luca)\
The problem is that when a chunk is lost, the first correctly received
frame after the chunk cannot be decoded correctly (because of missing
reference frames). libavcodec does not apply any error concealing here,
and NULL is returned as a decoded frame. Since the frame is correctly
received, the refiller does not substitute it with any duplicate... But
at the end the frame is missing, because it is received but not decoded!
This results in a wrong number of frames in the reconstructed stream.