[PATCH 3/5] alpm_list: abort on memory allocation failure
This makes it possible to detect a failure in several alpm_list
functions. Previously these functions would continue after a failure,
returning partial results and potentially leaking memory.
Unfortunately, NULL is a valid return value for the affected functions
if the input list is empty, so they still do not have a dedicated error
value. Callers can at least detect an error by checking if the input
list was empty.