bin/52615: fmt(1) trashes unicode strings

[coypu%sdf.org@localhost]

>Number:         52615
>Category:       bin
>Synopsis:       fmt(1) trashes unicode strings
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Oct 12 22:30:00 +0000 2017
>Originator:     coypu
>Release:        NetBSD 8.99.3
>Organization:
>Environment:
NetBSD localhost 8.99.3 NetBSD 8.99.3 (GENERIC) #11: Mon Oct  9 20:44:05 IDT 2017  fly@localhost:/home/fly/obj/sys/arch/amd64/compile/GENERIC amd64

>Description:

>How-To-Repeat:
$ export LC_ALL=en_US.UTF-8; locale; echo "בדיקה" > bdika; fmt bdika > bdika2; diff -u bdika bdika2
LANG=""
LC_CTYPE="en_US.UTF-8"
LC_COLLATE="C"
LC_TIME="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_ALL="en_US.UTF-8"
--- bdika	2017-10-13 01:15:28.072105486 +0300
+++ bdika2	2017-10-13 01:15:28.073959672 +0300
@@ -1 +1 @@
-בדיקה
+×××ק×


diff should not output anything.
>Fix: