Do not wrap exception into ISE on reaching max attempts

mirai-core/src/commonMain/kotlin/network/handler/selector/AbstractKeepAliveNetworkHandlerSelector.kt

@@ -76,10 +76,7 @@ internal abstract class AbstractKeepAliveNetworkHandlerSelector<H : NetworkHandl
 
         private tailrec suspend fun runImpl(): H {
             if (attempted >= maxAttempts) {
-                throw IllegalStateException(
+                throw exceptionCollector.getLast() ?: MaxAttemptsReachedException(null)
-                    "Failed to resume instance. Maximum attempts reached.",
-                    exceptionCollector.getLast()
-                )
             }
             yield() // Avoid endless recursion.
             val current = getCurrentInstanceOrNull()

mirai-core/src/commonMain/kotlin/network/handler/selector/MaxAttemptsReachedException.kt

@@ -0,0 +1,14 @@
+/*
+ * Copyright 2019-2021 Mamoe Technologies and contributors.
+ *
+ *  此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ *  Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ *  https://github.com/mamoe/mirai/blob/master/LICENSE
+ */
+
+package net.mamoe.mirai.internal.network.handler.selector
+
+internal data class MaxAttemptsReachedException(
+    override val cause: Throwable?
+) : IllegalStateException("Failed to resume instance. Maximum attempts reached.")

mirai-core/src/commonMain/kotlin/network/handler/selector/NetworkHandlerSelector.kt

@@ -40,6 +40,7 @@ internal interface NetworkHandlerSelector<H : NetworkHandler> {
      * Returned [H] can be in [NetworkHandler.State.OK] only (but it may happen that the state changed just after returning from this function).
      *
      * This function may throw exceptions, which would be propagated to the original caller of [SelectorNetworkHandler.resumeConnection].
+     * @throws MaxAttemptsReachedException
      */
     suspend fun awaitResumeInstance(): H
 }