TaskTree: Introduce CallDoneIf enum

Get rid of CustomTask c'tor taking 3 handlers.
If the done handler needs to be called only on
success or an error, add explicit 3rd arg of CallDoneIf type.

Task-number: QTCREATORBUG-29834
Change-Id: I10e55415587e6cac46620dd5177ad8269584583c
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/debugger/loadcoredialog.cpp

@@ -252,12 +252,14 @@ void AttachCoreDialog::accepted()
         parallel,
         AsyncTask<ResultType>{[=](auto &task) {
                               task.setConcurrentCallData(copyFileAsync, this->coreFile());
-                          },
-                          [=](const auto &task) { d->coreFileResult = task.result(); }},
+                              },
+                              [=](const auto &task) { d->coreFileResult = task.result(); },
+                              CallDoneIf::Success},
         AsyncTask<ResultType>{[=](auto &task) {
                               task.setConcurrentCallData(copyFileAsync, this->symbolFile());
-                          },
-                          [=](const auto &task) { d->symbolFileResult = task.result(); }},
+                              },
+                              [=](const auto &task) { d->symbolFileResult = task.result(); },
+                              CallDoneIf::Success}
     };
 
     d->taskTree.setRecipe(root);