CCodecBuffers: fix null buffer PCM conversion

EOS w/ null buffer may be queued, and it needs to go through the
conversion processing to keep the converted format.

Bug: 228576052
Test: atest ccodec_unit_test
Merged-In: I8503132a779aae6bc652ea030d29fc466c8a31a9
Change-Id: I8503132a779aae6bc652ea030d29fc466c8a31a9
2 files changed