Fix call to non-existing newEmptyValue() in PhabricatorDashboardPortalProfileMenuEngine
Summary:
`PhabricatorDashboardPortalProfileMenuEngine` calls `$this->newEmptyValue()` but neither `PhabricatorDashboardPortalProfileMenuEngine` nor its parent `PhabricatorProfileMenuEngine` define a `newEmptyValue()` method.
Thus use existing `newNoContentView()` in parent `PhabricatorProfileMenuEngine` (which according to its string output is supposed to cover this case).
Test Plan:
Go to a Portal with no content. Before applying the patch, Phorge shows the message defined in the parent class `PhabricatorProfileMenuEngine`: `No Content`; `No visible menu items can render content.`
After applying this change, it correctly shows the message defined in `PhabricatorDashboardPortalProfileMenuEngine`: `No Portal Content`; `None of the visible menu items in this portal can render any content.`
Reviewers: O1 Blessed Committers, speck
Reviewed By: O1 Blessed Committers, speck
Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D25648