* lisp/org-agenda.el: Do not modify string constant " "

(org-agenda-highlight-todo): Use `propertize' that copies the argument
string instead of `org-add-props'.  Otherwise, if the compiler
optimizes string constants into a single object, the properties may
populate in unexpected places.

Reported-by: Gustavo Barros <gusbrs.2016@gmail.com>
Link: https://orgmode.org/list/CAM9ALR95F_ZHV2_WsqAz0-35-S2rwxbHqsA5VGftvq51Yz3ZAQ@mail.gmail.com

lisp/org-agenda.el

@@ -7724,8 +7724,7 @@ The optional argument TYPE tells the agenda type."
                    (unless (string= org-agenda-todo-keyword-format "")
                      ;; Remove `display' property as the icon could leak
                      ;; on the white space.
-                     (org-add-props " " (org-plist-delete (text-properties-at 0 x)
-                                                          'display)))
+                     (apply #'propertize " " (org-plist-delete (text-properties-at 0 x) 'display)))
                    (substring x (match-end 3)))))))
       x)))