liblzma: Fix a memory leak in stream_encoder.c.
liblzma: Fix a memory leak in stream_encoder.c.

It leaks old filter options structures (hundred bytes or so)
every time the lzma_stream is reinitialized. With the xz tool,
this happens when compressing multiple files.

pombreda/go-liblzma,pombreda/go-liblzma,pombreda/go-liblzma