Add hard stops on empty batch edit sets

Summary:
Ref T8637. If a user tries to batch edit a list of tasks which can't be edited, we fall through to `withIDs(array())`, which can affect //everything//.

Explicitly stop batch editing if we don't have valid IDs or valid tasks.

The UI sort-of warns you that something is wrong, but this is ultimately a pretty severe UX issue. I'll fix the underlying Query in the next diff.

Test Plan: Tried to batch edit a list of tasks I didn't have permission to edit.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: lloyd.oliver, epriestley

Maniphest Tasks: T8637

Differential Revision: https://secure.phabricator.com/D13388

src/applications/maniphest/controller/ManiphestBatchEditController.php

@@ -25,6 +25,12 @@ final class ManiphestBatchEditController extends ManiphestController {
       $task_ids = $request->getStrList('batch');
     }
 
+    if (!$task_ids) {
+      throw new Exception(
+        pht(
+          'No tasks are selected.'));
+    }
+
     $tasks = id(new ManiphestTaskQuery())
       ->setViewer($viewer)
       ->withIDs($task_ids)
@@ -37,6 +43,12 @@ final class ManiphestBatchEditController extends ManiphestController {
       ->needProjectPHIDs(true)
       ->execute();
 
+    if (!$tasks) {
+      throw new Exception(
+        pht(
+          "You don't have permission to edit any of the selected tasks."));
+    }
+
     if ($project) {
       $cancel_uri = '/project/board/'.$project->getID().'/';
       $redirect_uri = $cancel_uri;