Safely handle block deletion (#13315)

Co-authored-by: Jude Melton-Houghton <jwmhjwmh@gmail.com>

src/server.cpp

@@ -666,6 +666,11 @@ void Server::AsyncRunStep(bool initial_step)
 			-1);
 	}
 
+	/*
+		Note: Orphan MapBlock ptrs become dangling after this call.
+	*/
+	m_env->getServerMap().step();
+
 	/*
 		Listen to the admin chat, if available
 	*/