bin/56472: mandoc does not complain about missing closes

[kim%netbsd.org@localhost (Kimmo Suominen)]

>Number:         56472
>Category:       bin
>Synopsis:       mandoc does not complain about missing closes
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Oct 28 10:20:00 +0000 2021
>Originator:     kim%netbsd.org@localhost (Kimmo Suominen)
>Release:        NetBSD 9.99.92 (202110262340Z)
>Organization:
>Environment:
System: NetBSD rendez-vous.gw.fi 9.99.92 NetBSD 9.99.92 (GENERIC) #0: Tue Oct 26 23:37:40 UTC 2021 mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:

	Running nroff on a document where an .It appears inside an open
	element (e.g. .So) results in an error:

	mdoc error: .It found in enclosing (e.g. .Ac ... .It ... .Ao) (#258)

	Running mandoc on the same document produces no such error.

	It would be helpful for mandoc to complain about any and all missing
	closes. (I feel that nroff is doing it here almost by accident.)

>How-To-Repeat:

	Obtain revision 1.31 of src/lib/libc/stdio/mktemp.3 and run it
	through nroff and mandoc.

	ftp -o mktemp.3 'http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/stdio/mktemp.3?rev=1.31'
	nroff -mdoc mktemp.3
	mandoc mktemp.3

>Fix: