strings: Map produces invalid utf-8 when passed PAD (U+0080) [1.10 backport]

[gopherbot]

@anupcshan requested issue #25242 to be considered for backport to the next 1.10 minor release.

@gopherbot Please consider this for backport to 1.10, it's a regression.

[msolo-dropbox]

This does seem worthy of backport. It looks like the whole 1.9 branch also has this issue which means that anyone on 1.8 or before has to skip two full release cycles, or start maintaining a fork.

What is the likelihood this will be included in 1.10.3?

[rsc]

@msolo-dropbox, seems likely to me, since the fix was committed on master and this issue exists.
@andybons, can this be backported to Go 1.9 too please?

[gopherbot]

Change https://golang.org/cl/114635 mentions this issue: [release-branch.go1.10] strings: fix encoding of \u0080 in map