patch 8.0.1384: not enough quickfix help; confusing winid

Problem:    Not enough quickfix help; confusing winid.
Solution:   Add more examples in the help. When the quickfix window is not
            present, return zero for getqflist() with 'winid'. Add more tests
            for jumping to quickfix list entries. (Yegappan Lakshmanan, closes
            #2427)
diff --git a/src/quickfix.c b/src/quickfix.c
index 0e488f1..fbf8a94 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -4949,9 +4949,12 @@
     if ((status == OK) && (flags & QF_GETLIST_WINID))
     {
 	win_T	*win;
+	int	win_id = 0;
+
 	win = qf_find_win(qi);
 	if (win != NULL)
-	    status = dict_add_nr_str(retdict, "winid", win->w_id, NULL);
+	    win_id = win->w_id;
+	status = dict_add_nr_str(retdict, "winid", win_id, NULL);
     }
     if ((status == OK) && (flags & QF_GETLIST_ITEMS))
     {