emacs-29 3fff22eb20c: Fix spell-checking email message with citations

[Eli Zaretskii]

branch: emacs-29
commit 3fff22eb20cc59c730c7ec4560c8663dfd55147b
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Fix spell-checking email message with citations
    
    This became broken 7 years ago, when the 'boundp condition was
    removed, and with it an important unrelated part of the code.
    * lisp/textmodes/ispell.el (ispell-message): Fix cite-regexp.
---
 lisp/textmodes/ispell.el | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lisp/textmodes/ispell.el b/lisp/textmodes/ispell.el
index eb550b639a3..48d48b07937 100644
--- a/lisp/textmodes/ispell.el
+++ b/lisp/textmodes/ispell.el
@@ -3973,7 +3973,8 @@ You can bind this to the key C-c i in GNUS or mail by 
adding to
                       (point-max)))
                    (t (min (point-max) (funcall ispell-message-text-end))))))
           (default-prefix   ; Vanilla cite prefix (just used for cite-regexp)
-            (if (ispell-non-empty-string mail-yank-prefix)
+            (if mail-yank-prefix
+                 (ispell-non-empty-string mail-yank-prefix)
               "   \\|\t"))
           (cite-regexp                 ;Prefix of quoted text
            (cond