patch 7.4.2300
Problem:    Get warning for deleting autocommand group when the autocommand
            using the group is scheduled for deletion. (Pavol Juhas)
Solution:   Check for deleted autocommand.
diff --git a/src/fileio.c b/src/fileio.c
index 9ae46fa..6bf5452 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -8018,7 +8018,7 @@
 					    event = (event_T)((int)event + 1))
 	{
 	    for (ap = first_autopat[(int)event]; ap != NULL; ap = ap->next)
-		if (ap->group == i)
+		if (ap->group == i && ap->pat != NULL)
 		{
 		    give_warning((char_u *)_("W19: Deleting augroup that is still in use"), TRUE);
 		    in_use = TRUE;