org-element--cache-before-change: Fix edge case creating heading

* lisp/org-element.el (org-element--cache-before-change): Fix edge
case when a heading is created because we insert a newline right
before ****.
* testing/lisp/test-org-element.el (test-org-element/cache-headline):
Add tests.

Reported-by: Rodrigo Morales <moralesrodrigo1100@gmail.com>
Link: https://orgmode.org/list/CAGxMbPbbqc33iaqJ=EceyKrLaf4maJAxaUmJGaPOvG_Rpw+xcQ@mail.gmail.com

lisp/org-element.el

@@ -6705,20 +6705,8 @@ The function returns the new value of `org-element--cache-change-warning'."
        (setq org-element--cache-change-tic (buffer-chars-modified-tick))
        (setq org-element--cache-last-buffer-size (buffer-size))
        (goto-char beg)
-       (beginning-of-line)
-       (let ((bottom (save-excursion
-                       (goto-char end)
-                       (if (and (bolp)
-                                ;; When beg == end, still extent to eol.
-                                (> (point) beg))
-                           ;; FIXME: Potential pitfall.
-                           ;; We are appending to an element end.
-                           ;; Unless the last inserted char is not
-                           ;; newline, the next element is not broken
-                           ;; and does not need to be purged from the
-                           ;; cache.
-                           end
-                         (line-end-position)))))
+       (forward-line 0)
+       (let ((bottom (save-excursion (goto-char end) (line-end-position))))
          (prog1
              ;; Use the worst change warning to not miss important edits.
              ;; This function is called before edit and after edit by

testing/lisp/test-org-element.el

@@ -4372,7 +4372,32 @@ paragraph
     (let ((org-element-use-cache t))
       (org-element-at-point (point-max))
       (delete-region (point) (point-max))
-      (should (eq 'paragraph (org-element-type (org-element-at-point)))))))
+      (should (eq 'paragraph (org-element-type (org-element-at-point))))))
+  ;; Remove/re-introduce heading.
+  (org-test-with-temp-text
+      "
+* 1
+** 1-1
+a
+<point>** 1-2
+a
+"
+    (let ((org-element-use-cache t))
+      (org-element-at-point (point-max))
+      (insert "FOO")
+      (should
+       (equal
+        "1-1"
+        (org-element-property
+         :title
+         (org-element-lineage (org-element-at-point) '(headline)))))
+      (insert "\n")
+      (should
+       (equal
+        "1"
+        (org-element-property
+         :title
+         (org-element-lineage (org-element-at-point) '(headline))))))))
 
 (provide 'test-org-element)