Remove ID and CUSTOM_ID properties when inserting checklist template

When the template associated with the item at point contains sub-items itself,
those may have been assigned ID or CUSTOM_ID properties.  Copying the template
would thus duplicate these properties, violating their implicit uniqueness
constraint, so we now remove those properties from the inserted checklist
template.

site-lisp/db-org.el

@@ -1090,6 +1090,9 @@ inserting the checklist."
 
         (t ;; Default action: insert complete checklist.
 
+         (let (point-before-template
+               point-after-template)
+
            ;; Let's remember where we are, so that latter on CHECKLIST_INSERTED_P
            ;; will be inserted at the original heading (where we are now) and not
            ;; at possible new subtrees coming from the template.
@@ -1147,12 +1150,29 @@ inserting the checklist."
              ;; Insert template, when avilable.
              (let ((template-marker (db/org--find-template)))
                (insert "\n\nTemplate:")
+               (setq point-before-template (point))
                (if (not template-marker)
                    (insert " none.\n")
-               (db/org-copy-body-from-item-to-point template-marker))))
+                 (db/org-copy-body-from-item-to-point template-marker))
+               (setq point-after-template (point))))
 
            (org-entry-put (point) "CHECKLIST_INSERTED_P" "t")
-         (db/org-goto-first-open-checkbox-in-subtree))))
+           (org-update-statistics-cookies nil)
+
+           ;; Remove any existing ID properties, as they would be duplicates
+           ;; now.  Only do this in the part inserted with template, though, and
+           ;; leave previously existing child items and the item itself as they
+           ;; are.
+           (save-mark-and-excursion
+             (set-mark point-before-template)
+             (goto-char point-after-template)
+             (org-map-entries #'(lambda ()
+                                  (org-entry-delete (point) "ID")
+                                  (org-entry-delete (point) "CUSTOM_ID"))
+                              nil
+                              'region))
+
+           (db/org-goto-first-open-checkbox-in-subtree)))))
 
 (define-obsolete-function-alias 'db/org-copy-template
   'db/org-insert-checklist
@@ -1183,6 +1203,7 @@ inserted template."
   (unless (number-or-marker-p pom)
     (user-error "Argument is neither point nor mark: %s" pom))
   (let ((body (save-restriction
+                (widen)
                 (save-mark-and-excursion
                   (let ((template-element (org-with-point-at pom
                                             (org-element-at-point))))
@@ -1224,9 +1245,7 @@ inserted template."
     (unless (save-mark-and-excursion
               (forward-line 1)
               (looking-at (rx bol (* space) eol)))
-      (insert "\n"))
-
-    (org-update-statistics-cookies nil)))
+      (insert "\n"))))
 
 (defun db/org-goto-first-open-checkbox-in-subtree (&optional silent)
   "Jump to first open checkbox in the current subtree.