Fix native-mt awaitAll

Fixes #2025

Author: elizarov

kotlinx-coroutines-core/common/src/Await.kt

@@ -83,15 +83,18 @@ private class AwaitAll<T>(private val deferreds: Array<out Deferred<T>>) {
 
     private inner class DisposeHandlersOnCancel(private val nodes: Array<AwaitAllNode>) : CancelHandler() {
         fun disposeAll() {
-            nodes.forEach { it.handle.dispose() }
+            nodes.forEach { it.handle!!.dispose() }
         }
 
         override fun invoke(cause: Throwable?) { disposeAll() }
         override fun toString(): String = "DisposeHandlersOnCancel[$nodes]"
     }
 
     private inner class AwaitAllNode(private val continuation: CancellableContinuation<List<T>>, job: Job) : JobNode<Job>(job) {
-        lateinit var handle: DisposableHandle
+        private val _handle = atomic<DisposableHandle?>(null)
+        var handle: DisposableHandle?
+            get() = _handle.value
+            set(value) { _handle.value = value }
 
         private val _disposer = atomic<DisposeHandlersOnCancel?>(null)
         var disposer: DisposeHandlersOnCancel?

kotlinx-coroutines-core/native/test/WorkerDispatcherTest.kt

@@ -313,5 +313,18 @@ class WorkerDispatcherTest : TestBase() {
         finish(6)
     }
 
+    @Test
+    fun testAwaitAll() = runTest {
+        expect(1)
+        val d1 = async(dispatcher) {
+            "A"
+        }
+        val d2 = async(dispatcher) {
+            "B"
+        }
+        assertEquals("AB", awaitAll(d1, d2).joinToString(""))
+        finish(2)
+    }
+
     private data class Data(val s: String)
 }