org-list: fix infinite loop on erroneous block and drawer constructs

* lisp/org-list.el (org-list-struct,org-in-item-p): don't assume end
  of blocks or drawers necessarily start somewhere. It it isn't the
  case, treat them as normal text.

lisp/org-list.el

@@ -468,10 +468,10 @@ This checks `org-list-ending-method'."
 		     (looking-at org-list-end-re))
 		(throw 'exit nil))
 	       ;; Skip blocks, drawers, inline-tasks, blank lines
-	       ((looking-at "^[ \t]*#\\+end_")
-		(re-search-backward "^[ \t]*#\\+begin_" nil t))
-	       ((looking-at "^[ \t]*:END:")
-		(re-search-backward drawers-re nil t)
+	       ((and (looking-at "^[ \t]*#\\+end_")
+		     (re-search-backward "^[ \t]*#\\+begin_" lim-up t)))
+	       ((and (looking-at "^[ \t]*:END:")
+		     (re-search-backward drawers-re lim-up t))
 		(beginning-of-line))
 	       ((and inlinetask-re (looking-at inlinetask-re))
 		(org-inlinetask-goto-beginning)
@@ -689,10 +689,10 @@ Assume point is at an item."
 			     (memq (assq (car beg-cell) itm-lst) itm-lst))))
 	       ;; Skip blocks, drawers, inline tasks, blank lines
 	       ;; along the way.
-	       ((looking-at "^[ \t]*#\\+end_")
-		(re-search-backward "^[ \t]*#\\+begin_" nil t))
-	       ((looking-at "^[ \t]*:END:")
-		(re-search-backward drawers-re nil t)
+	       ((and (looking-at "^[ \t]*#\\+end_")
+		     (re-search-backward "^[ \t]*#\\+begin_" lim-up t)))
+	       ((and (looking-at "^[ \t]*:END:")
+		     (re-search-backward drawers-re lim-up t))
 		(beginning-of-line))
 	       ((and inlinetask-re (looking-at inlinetask-re))
 		(org-inlinetask-goto-beginning)
@@ -756,11 +756,11 @@ Assume point is at an item."
 	      (throw 'exit (push (cons 0 (point)) end-lst-2)))
 	     ;; Skip blocks, drawers, inline tasks and blank lines
 	     ;; along the way
-	     ((looking-at "^[ \t]*#\\+begin_")
-	      (re-search-forward "^[ \t]*#\\+end_")
+	     ((and (looking-at "^[ \t]*#\\+begin_")
+		   (re-search-forward "^[ \t]*#\\+end_" lim-down t))
 	      (forward-line 1))
-	     ((looking-at drawers-re)
-	      (re-search-forward "^[ \t]*:END:" nil t)
+	     ((and (looking-at drawers-re)
+		   (re-search-forward "^[ \t]*:END:" lim-down t))
 	      (forward-line 1))
 	     ((and inlinetask-re (looking-at inlinetask-re))
 	      (org-inlinetask-goto-end))