mime/multipart: test for presence of filename instead of content-type
Fixes #24041
Preserving the intended fix in https://go.googlesource.com/go/+/
81ec7256072ed5e20b8827c583193258769aebc0
Change-Id: I600d3d7edc74ca072a066739e2ef3235877d808f
GitHub-Last-Rev:
14973d7c2bf4022c28ef4b4984ec3cd352c1d4d8
GitHub-Pull-Request: golang/go#24104
Reviewed-on: https://go-review.googlesource.com/96975
Reviewed-by: Andrew Bonventre <andybons@golang.org>
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>