Fix resolving symlinks in Eshell history file names

* lisp/eshell/em-dirs.el (eshell-write-last-dir-ring):
* lisp/eshell/em-hist.el (eshell-write-history): Don't call
file-truename with argument of nil.  (Bug#33477)

* test/lisp/eshell/eshell-tests.el (with-temp-eshell): Remove
HISTFILE from the environment, to make sure the Eshell history
file is nil.

lisp/eshell/em-dirs.el

@@ -553,7 +553,7 @@ in the minibuffer:
 (defun eshell-write-last-dir-ring ()
   "Write the buffer's `eshell-last-dir-ring' to a history file."
   (let* ((file eshell-last-dir-ring-file-name)
-	 (resolved-file (file-truename file)))
+	 (resolved-file (if (stringp file) (file-truename file))))
     (cond
      ((or (null file)
 	  (equal file "")

lisp/eshell/em-hist.el

@@ -467,7 +467,7 @@ Useful within process sentinels.
 
 See also `eshell-read-history'."
   (let* ((file (or filename eshell-history-file-name))
-	 (resolved-file (file-truename file)))
+	 (resolved-file (if (stringp file) (file-truename file))))
     (cond
      ((or (null file)
 	  (equal file "")

test/lisp/eshell/eshell-tests.el

@@ -31,6 +31,9 @@
 (defmacro with-temp-eshell (&rest body)
   "Evaluate BODY in a temporary Eshell buffer."
   `(let* ((eshell-directory-name (make-temp-file "eshell" t))
+          ;; We want no history file, so prevent Eshell from falling
+          ;; back on $HISTFILE.
+          (_ (setenv "HISTFILE"))
           (eshell-history-file-name nil)
           (eshell-buffer (eshell t)))
      (unwind-protect