mktree: fix a memory leak in write_tree()
mktree: fix a memory leak in write_tree()

We forget to call strbuf_release to release the buf memory.

Signed-off-by: Liu Yuan <12f958e627733f4b5d561b914fd29a73f5c3a02b@taobao.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git