org-table.el: Fix a bug when displaying a table header

* lisp/org-table.el (org-table-row-get-visible-string): Fix wrong
beginning of the header string.
(org-table-header-set-header): Get the real beginning of the line.

Reported-by: "Oorja Sandhu" <oorja.sandhu@inoutbox.com>
Link: https://orgmode.org/list/7beea3b5-6fe5-4ba6-831e-19a88d87de6b@www.fastmail.com/

lisp/org-table.el

@@ -461,13 +461,14 @@ This may be useful when columns have been shrunk."
     (when pos (goto-char pos))
     (goto-char (line-beginning-position))
     (let ((end (line-end-position)) str)
+      (backward-char)
       (while (progn (forward-char 1) (< (point) end))
 	(let ((ov (car (overlays-at (point)))))
 	  (if (not ov)
 	      (push (char-to-string (char-after)) str)
 	    (push (overlay-get ov 'display) str)
 	    (goto-char (1- (overlay-end ov))))))
-      (format "|%s" (mapconcat #'identity (reverse str) "")))))
+      (format "%s" (mapconcat #'identity (reverse str) "")))))
 
 (defvar-local org-table-header-overlay nil)
 (defun org-table-header-set-header ()
@@ -483,7 +484,7 @@ This may be useful when columns have been shrunk."
                         (while (or (org-at-table-hline-p)
                                    (looking-at-p ".*|\\s-+<[rcl]?\\([0-9]+\\)?>"))
                           (move-beginning-of-line 2))
-                        (point)))
+                        (line-beginning-position)))
                  (end (save-excursion (goto-char beg) (point-at-eol))))
             (if (pos-visible-in-window-p beg)
                 (when (overlayp org-table-header-overlay)