cccombiner: fix CDP padding detection
While a cc_data_pkt with cc_valid 0 should be considered padding, it might be followed up by valid DTVCC packets, and should not cause the whole CDP packet to get discarded.
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While a cc_data_pkt with cc_valid 0 should be considered padding, it might be followed up by valid DTVCC packets, and should not cause the whole CDP packet to get discarded.