libext2fs: Fix memory leak in the Unix I/O layer when changing block size

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index 8c599aa..78a1d1c 100644
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -302,6 +302,8 @@
 		cache->access_time = 0;
 		cache->dirty = 0;
 		cache->in_use = 0;
+		if (cache->buf)
+			ext2fs_free_mem(&cache->buf);
 		if ((retval = ext2fs_get_mem(channel->block_size,
 					     &cache->buf)))
 			return retval;