bug#70322: 30.0.50; format-seconds with %z doesn't handle zero input correctly

[Eli Zaretskii <eliz@gnu.org>]

> From: Herman@debbugs.gnu.org, Géza <geza.herman@gmail.com>
> Date: Wed, 10 Apr 2024 11:59:42 +0200
> 
> 
> When the input seconds is 0, format-seconds emits the full string. For
> example,
> 
> (format-seconds "%Y, %D, %H, %M, %z%S" 0)
> 
> returns "0 years, 0 days, 0 hours, 0 minutes, 0 seconds"
> 
> instead of "0 seconds".
> 
> (format-seconds "%Y, %D, %H, %M, %z%S" 1) correctly returns "1 second".

Does the patch below give good results?

diff --git a/lisp/calendar/time-date.el b/lisp/calendar/time-date.el
index e96e2e7..b75f17c 100644
--- a/lisp/calendar/time-date.el
+++ b/lisp/calendar/time-date.el
@@ -344,8 +344,11 @@ format-seconds
              string)
         (cond
          ((string-equal spec "z")
-          (setq chop-leading (and leading-zeropos
-                                  (min leading-zeropos (match-beginning 0)))))
+          (setq chop-leading
+                (if leading-zeropos
+                    (min leading-zeropos (match-beginning 0))
+                  ;; The entire speci is zero, get past "%z" to last 0.
+                  (+ 2 (match-beginning 0)))))
          ((string-equal spec "x")
           (setq chop-trailing t))
          (t