inside table, delete-backward-char must not insert spaces when overwrite mode is on

* lisp/org.el (org-delete-backward-char): check for nil overwrite-mode before inserting
spaces.

TINYCHANGE

There's probably a different/better way to do this, but this seemed the least intrusive.
This patch is in the public domain.

lisp/org.el

@@ -16574,9 +16574,11 @@ because, in this case the deletion might narrow the column."
 	    (noalign (looking-at "[^|\n\r]*  |"))
 	    (c org-table-may-need-update))
 	(backward-delete-char N)
-	(skip-chars-forward "^|")
-	(insert " ")
-	(goto-char (1- pos))
+	(if (not overwrite-mode)
+	    (progn
+	      (skip-chars-forward "^|")
+	      (insert " ")
+	      (goto-char (1- pos))))
 	;; noalign: if there were two spaces at the end, this field
 	;; does not determine the width of the column.
 	(if noalign (setq org-table-may-need-update c)))