Check SYNCD size before filling partial MPEG-TS packet

[Silverlined]

https://github.com/igorauad/gr-dvbs2rx/blob/c22b350912f31d87e397ef3ff470ac81cef943e0/lib/bbdeheader_bb_impl.cc#L205

The logic inside this scope assumes sequential BB frames. It will break and synchronization will be lost if a BB frame has been dropped.

I would propose including the following to check whether the SYNCD size corresponds to the remaining size of the partial TS packet.

        if (d_partial_ts_bytes && ((d_bbheader.syncd / 8) != TS_PACKET_LENGTH - 1 - d_partial_ts_bytes)) {
            GR_LOG_DEBUG_LEVEL(3, "Not enough bytes to complete the partial TS packet.");
            d_packet_drop_cnt++;
            d_synched = false;
        }

This would be added before evaluating the d_synched in: https://github.com/igorauad/gr-dvbs2rx/blob/c22b350912f31d87e397ef3ff470ac81cef943e0/lib/bbdeheader_bb_impl.cc#L193