fix weed.Delete() crash bugs.

[chennqqi]

a http post can be closed only if a resp is valid

This hanppend when an fid not exist or removed already.

[ginuerzh]

I think it should be defer resp.Close() if no error occurred, no matter whether http.StatusCode is StatusOK.

[chennqqi]

@ginuerzh You're right. but call resp.Close() must judge if http.Do returned an error. I update defer resp.Close() before whether http.StatusCode is StatusOK.