MINOR: chunks: Use dedicated function to init/deinit trash buffers

MINOR: chunks: Use dedicated function to init/deinit trash buffers

Now, we use init_trash_buffers and deinit_trash_buffers to, respectively,
initialize and deinitialize trash buffers (trash, trash_buf1 and trash_buf2).

These functions have been introduced to be used by threads, to deal with
thread-local trash buffers.