Fix a memory leak in test_index.c.
Fix a memory leak in test_index.c.

This was introduced in
bd13b04e202b6f495a68eb0766f97085b7c50a06.

Thanks to Jim Meyering for noticing it.

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