Fix `awaitDisconnection()`

mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/QQAndroidBotNetworkHandler.kt

@@ -531,5 +531,5 @@ internal class QQAndroidBotNetworkHandler(bot: QQAndroidBot) : BotNetworkHandler
         super.close(cause)
     }
 
-    override suspend fun awaitDisconnection() = _packetReceiverJob?.join() ?: Unit
+    override suspend fun awaitDisconnection() = supervisor.join()
 }