When PLC data was produced due to underrun and decode buffer has reached
target level, drop received audio if we already did PLC for that packet.
It's better to lose some packets than having to resync latency.
When about to underrun when PLC is active, update rate matching before
filling up buffer, so that rate slows down and we do not get stuck in a
continuous underrun where PLC fills data and we drop received packets.
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