chore(backend): assert user joined

packages/backend/src/core/ReversiService.ts

@@ -295,6 +295,9 @@ export class ReversiService implements OnApplicationShutdown, OnModuleInit {
 			isLlotheo: false,
 			noIrregularRules: options.noIrregularRules,
 		}, { relations: ['user1', 'user2'] });
+		if (game.user1 === gane.user2) {
+			throw new Error('broken match');
+		}
 		this.cacheGame(game);
 
 		const packed = await this.reversiGameEntityService.packDetail(game);