patch 7.4.1647
Problem: Using freed memory after setqflist() and ":caddbuffer". (Dominique)
Solution: Set qf_ptr when adding the first item to the quickfix list.
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index 667ece4..e56c8a2 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -679,3 +679,11 @@
call XquickfixChangedByAutocmd('c')
call XquickfixChangedByAutocmd('l')
endfunction
+
+func Test_caddbuffer_to_empty()
+ helpgr quickfix
+ call setqflist([], 'r')
+ cad
+ call assert_fails('cn', 'E553:')
+ quit!
+endfunc