Prevent segfault when all todo items are hidden

To prevent from illegal memory access, we checked whether the list of
todo items is empty before performing an interactive todo item action
such as flagging or removal. However, since 1a4bf2b (Add a "hide
completed" view to the todo panel, 2016-01-17), it is possible to hide
completed items from the todo panel. Thus, it may occur that the todo
list box is empty while the list of todo items is not.

To detect such situations as well, teach todo_get_item() to return NULL
if the requested item does not exist. Then, instead of checking whether
the todo item list is non-empty, make sure that the item returned by
todo_get_item() is non-NULL when performing an action.

Reported-by: Vlad Glagolev <scm@vaygr.net>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/todo.c b/src/todo.c
index 9a6f72f..8027803 100644
--- a/src/todo.c
+++ b/src/todo.c
@@ -59,6 +59,9 @@ struct todo *todo_get_item(int item_number, int skip_completed)
 	else
 		i = LLIST_NTH(&todolist, item_number);
 
+	if (!i)
+		return NULL;
+
 	return LLIST_GET_DATA(i);
 }