File graphviz-null_dereference.patch of Package graphviz.15286

--- graphviz-2.28.0/lib/dotgen/conc.c.orig	2020-06-02 16:38:09.018747192 +0200
+++ graphviz-2.28.0/lib/dotgen/conc.c	2020-06-02 16:49:44.730480052 +0200
@@ -157,7 +157,7 @@
 
     for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
 	lead = GD_rankleader(g)[r];
-	if (GD_rank(agroot(g))[r].v[ND_order(lead)] != lead)
+	if (!lead || GD_rank(agroot(g))[r].v[ND_order(lead)] != lead)
 	    abort();
 	GD_rank(g)[r].v =
 	    GD_rank(agroot(g))[r].v + ND_order((GD_rankleader(g)[r]));