Bugfix: Protect line indentation in orgstruct-mode

(org-indent-line-function): Make sure this works even if there is not
`org-drawer-regexp' defined.  This can happen when orgstruct-mode is
used in a non-org buffer.

lisp/ChangeLog

@@ -9,6 +9,9 @@
 	(org-set-regexps-and-options, org-assign-fast-keys)
 	(org-fast-todo-selection, org-fast-tag-selection): Handle newline
 	option.
+	(org-indent-line-function): Make sure this works even if there is
+	not `org-drawer-regexp' defined.  This can happen when
+	orgstruct-mode is used in a non-org buffer.
 
 	* org-list.el (org-checkbox-blocked-p): New function.
 	(org-toggle-checkbox): Check for blocking.

lisp/org.el

@@ -14800,6 +14800,7 @@ which make use of the date at the cursor."
   (interactive)
   (let* ((pos (point))
 	 (itemp (org-at-item-p))
+	 (org-drawer-regexp (or org-drawer-regexp "\000"))
 	 column bpos bcol tpos tcol bullet btype bullet-type)
     ;; Find the previous relevant line
     (beginning-of-line 1)