[PATCH] Fix org-do-latex-and-related at buffer start

[Shao-yu Tseng <dev@notyourcomputer.net>]

When org-mode is called at the start of a buffer that starts with a
latex fragment, it produces an error "Beginning of buffer" caused by
attempt to call backward-char.

A minimal example to reproduce:
1. Open a scratch buffer
2. Insert text \(\Omega\)
3. Turn on org-mode

The observable effect of this bug is that org-export-string-as does not
work for strings beginning with a latex fragment, example:

(org-export-string-as "\\(\\Omega\\)" 'html t '(:with-toc nil))

This does not return an html string as expected

  #	modified:   lisp/org-src.el
---
 lisp/org-src.el | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lisp/org-src.el b/lisp/org-src.el
index 4b05789c6..e754feb41 100644
--- a/lisp/org-src.el
+++ b/lisp/org-src.el
@@ -744,7 +744,7 @@ as `org-src-fontify-natively' is non-nil."
       (goto-char start)
       (let ((indent-offset
 	     (if (org-src-preserve-indentation-p) 0
-	       (+ (progn (backward-char)
+	       (+ (progn (when (> (point) (point-min)) (backward-char))
                          (org-current-text-indentation))
 	          org-edit-src-content-indentation))))
         (while (re-search-forward "^[ ]*\t" end t)
-- 
2.47.1