[release-branch.go1.7] net/http: multipart ReadForm close file after copy
[release-branch.go1.7] net/http: multipart ReadForm close file after copy

Always close the file regardless of whether the copy succeeds or fails.
Pass along the close error if the copy succeeds

Updates #16296
Fixes #17965

Change-Id: Ib394655b91d25750f029f17b3846d985f673fb50
Reviewed-on: https://go-review.googlesource.com/30410
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-on: https://go-review.googlesource.com/33639
Reviewed-by: Chris Broadfoot <0c2851a4f8ab4aa5606e69c0757771dd13dbe686@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go