When a viewer is not logged in and opens a public dashboard which embeds a query panel whose data requires a Current Viewer context (e.g. assigned or authored tasks, or joined projects), do not throw an exception but show an explanatory placeholder sentence (similar to already existing 'No tasks found.' or 'No documents found.' strings).
EXCEPTION: (Exception) Query "assigned" is unknown to application search engine "ManiphestTaskSearchEngine"! at [<phorge>/src/applications/dashboard/paneltype/PhabricatorDashboardQueryPanelType.php:80] EXCEPTION: (Exception) Query "joined" is unknown to application search engine "PhabricatorProjectSearchEngine"! at [<phorge>/src/applications/dashboard/paneltype/PhabricatorDashboardQueryPanelType.php:80]
Closes T15792