mime/multipart/partReader ignores first EOF it reads and fails if next Read call returns another error

[AsamK]

1. What version of Go are you using (go version)?
   go1.6
2. What operating system and processor architecture are you using (go env)?
   linux/amd64
3. What did you do?
   https://play.golang.org/p/ePzW9GtCEe
4. What did you expect to see?
   the multipart reader should correctly read the multipart content
5. What did you see instead?
   ReadForm() fails with "multipart: Part Read: unexpected EOF"

This worked in go1.5 and fails in go1.6 because of a change in the zlib reader (see #14675)

[gopherbot]

CL https://golang.org/cl/20297 mentions this issue.

[bradfitz]

Re-milestoning for consideration for Go 1.6.1. This bug was always present, but was exposed by #14675. If #14675 goes into Go 1.6.1, that might be enough. Although this fix is trivial too.

[gopherbot]

CL https://golang.org/cl/22045 mentions this issue.