pbx_dundi: reordered unloading of module pbx_dundi

Destroy scheduler after peers are pruned to stop dundi crashing when
unloading module.

ASTERISK-26987
Reported-by: Kirsty Tyerman

Change-Id: Ic12e562cd90d8d813a9e97f302045091f59e3c05

pbx/pbx_dundi.c

@@ -4982,13 +4982,14 @@ static int unload_module(void)
 
 	close(netsocket);
 	io_context_destroy(io);
-	ast_sched_context_destroy(sched);
 
 	mark_mappings();
 	prune_mappings();
 	mark_peers();
 	prune_peers();
 
+	ast_sched_context_destroy(sched);
+
 	return 0;
 }