TaskTree: Fix progress value on synchronous error

Add a test for it.

Change-Id: I86a1cf89efaef88b152c9db274ea712381cad407
Reviewed-by: hjk <hjk@qt.io>

src/libs/solutions/tasking/tasktree.cpp

@@ -2271,6 +2271,7 @@ void TaskTreePrivate::startChildren(RuntimeContainer *container)
         if (task->m_setupResult == SetupResult::Continue)
             continue;
 
+        task->m_parentIteration->deleteChild(task.get());
         childDone(iteration, task->m_setupResult == SetupResult::StopWithSuccess);
         if (container->m_parentTask->m_setupResult != SetupResult::Continue)
             return;

tests/auto/solutions/tasking/tst_tasking.cpp

@@ -3009,6 +3009,25 @@ void tst_Tasking::testTree_data()
             << TestData{storage, root, {}, 1, DoneWith::Success, 0};
     }
 
+    {
+        class CustomTaskAdapter : public TaskAdapter<bool> // bool is dummy
+        {
+        private:
+            void start() final { emit done(DoneResult::Error); }
+        };
+
+        using CustomTask = CustomTask<CustomTaskAdapter>;
+
+        // Check if progress is updated correctly on error when the 1st task finishes synchonously.
+        const Group root {
+            storage,
+            CustomTask(),
+            createSuccessTask(1)
+        };
+        QTest::newRow("ProgressOnSynchronousError")
+            << TestData{storage, root, {}, 2, DoneWith::Error, 0};
+    }
+
     {
         const auto recipe = [storage, createSuccessTask](bool withTask) {
             return Group {