A malformed file (generated by AFL) had a 'samples_left_to_process' value
of greater than the actual numbe of samples. When re-encoding the decoder
would get to the end of the file and then continuously return a decode
status of FLAC__STREAM_DECODER_END_OF_STREAM, causing an infinite loop.

Solution is to break out of the loop on two consecutive end-of-stream
events.