android/hal-audio: Send packets only when data were encoded

android/hal-audio: Send packets only when data were encoded

Codec may not return encoded packet on every encode_mediapacket call,
i.e. in case there's not enough data it may buffer data and encode on
subsequent calls when enough data were provided. We need to make sure
media packet is written only in case somethind was encoded so we don't
send empty packets.