CCU: Ignore restricted child tasks for progress bar

If we have a child task which we can't access, ManiphestTaskQuery will
raise an exception; trying to view the workboard, this will bubble up as
a policy exception which will (incorrectly) tell the viewer they can't
access the project.

Catch any exceptions whilst trying to calculate overall progress, and
ignore those restricted child tasks.

src/applications/maniphest/storage/ManiphestTask.php

@@ -430,10 +430,17 @@ final class ManiphestTask extends ManiphestDAO
     $children = $this->loadDependsOnTaskPHIDs();
 
     foreach ($children as $child) {
-      $task = id(new ManiphestTaskQuery())
-        ->setViewer($viewer)
-        ->withPHIDs(array($child))
-        ->executeOne();
+      try {
+        $task = id(new ManiphestTaskQuery())
+          ->setViewer($viewer)
+          ->withPHIDs(array($child))
+          ->executeOne();
+      } catch (Exception $e) {
+        $task = null;
+      }
+      if (!$task) {
+        continue;
+      }
 
       $child_progress = $task->getTaskProgress($viewer);