patch 8.0.0565: using freed memory in :caddbuf

Problem:    Using freed memory in :caddbuf after clearing quickfix list.
            (Dominique Pelle)
Solution:   Set qf_last to NULL.

Author: brammool

src/quickfix.c

@@ -2750,6 +2750,7 @@ qf_free(qf_info_T *qi, int idx)
     vim_free(qi->qf_lists[idx].qf_title);
     qi->qf_lists[idx].qf_title = NULL;
     qi->qf_lists[idx].qf_index = 0;
+    qi->qf_lists[idx].qf_last = NULL;
 
     qf_clean_dir_stack(&qi->qf_dir_stack);
     qi->qf_directory = NULL;

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    565,
 /**/
     564,
 /**/