MediaCodec: reset size to zero for EOS.

testflush CTS test doesn't have logic to detect EOS. For EOS buffer,
input size from parser is -1, testflush CTS test sends this EOS buffer
without checking for valid input buffer size. MediaCodec rejects
this buffer, which results in testflush test failure.
To solve this reset the size to zero in Mediacodec if input buffer
size is invalid and EOS flag is set.

CRs-Fixed: 911338
Change-Id: I31727a00e0edf5604d0409fecbd976334508e6d7