Prevent crash on dst initialization failure

server might be created, but not yet fully initialized, when fatal
function is called. Check both server and task before attaching
exclusive task.

(cherry picked from commit c5e7152cf0)

bin/named/server.c

@@ -10128,7 +10128,7 @@ named_server_destroy(named_server_t **serverp) {
 
 static void
 fatal(named_server_t *server, const char *msg, isc_result_t result) {
-	if (server != NULL) {
+	if (server != NULL && server->task != NULL) {
 		/*
 		 * Prevent races between the OpenSSL on_exit registered
 		 * function and any other OpenSSL calls from other tasks