Re-fix use of strdup on a NULL pointer (re: 9a9da2c) (#718)

Thank you @lzaoral for debugging this issue and creating this
reproducer:

$ tty   # check that the shell is connected to a pseudoterminal
/dev/pts/4
$ mkdir /var/tmp/chroottest
$ dnf --releasever=39 --installroot=/var/tmp/chroottest install ksh
$ echo "/dev/udp/127.0.0.1/514;0;104" |
        sudo tee /var/tmp/chroottest/etc/ksh_audit
$ sudo chroot /var/tmp/chroottest /bin/ksh -lic 'exit 0'
(ksh segfaults)

Analysis: On Linux, ttyname(3)[*] may fail if:

* EBADF  Bad file descriptor.
* ENODEV fd refers to a slave pseudoterminal device but the
         corresponding pathname could not be found [...].
* ENOTTY fd does not refer to a terminal device.

Calling isatty(3) before ttyname(3) only prevents the first and
third cases.

src/cmd/ksh93/edit/history.c: sh_histinit():
- To catch the second case, let's call ttyname(2) directly, check
  for NULL and remove the redundant isatty() call.

[*] https://man7.org/linux/man-pages/man3/ttyname.3.html

NEWS

@@ -2,6 +2,11 @@ This documents significant changes in the dev branch of ksh 93u+m.
 For full details, see the git log at: https://github.com/ksh93/ksh
 Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 
+2024-02-08:
+
+- Fixed an init-time crash that may occur if standard error is on a terminal,
+  but the path to its tty device can't be found (e.g., in a chroot situation).
+
 2024-02-06:
 
 - Fixed a regression introduced on 2023-03-04 that caused ksh to lock up

src/cmd/ksh93/edit/history.c

@@ -15,6 +15,7 @@
 *            Johnothan King <[email protected]>             *
 *         hyenias <[email protected]>          *
 *                Govind Kamat <[email protected]>                 *
+*               Vincent Mihalkovic <[email protected]>               *
 *                                                                      *
 ***********************************************************************/
 /*
@@ -353,7 +354,8 @@ int  sh_histinit(void)
 			if(fd>=0)
 			{
 				fcntl(fd,F_SETFD,FD_CLOEXEC);
-				hp->tty = sh_strdup(isatty(2)?ttyname(2):"notty");
+				const char* tty = ttyname(2);
+				hp->tty = sh_strdup(tty?tty:"notty");
 				hp->auditfp = sfnew(NULL,NULL,-1,fd,SF_WRITE);
 			}
 		}

src/cmd/ksh93/include/version.h

@@ -18,7 +18,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.1.0-alpha"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2024-02-06"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2024-02-08"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2024 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */