Do not throw an exception when passing bogus parameter string values to hovercards. Instead, just convert to an empty array.
In consequence, see a proper hovercard correctly displaying Unknown Object (????) instead of an exception:
EXCEPTION: (TypeError) idx(): Argument #1 ($array) must be of type array, string given, called in /var/www/html/phorge/phorge/src/applications/search/controller/PhabricatorSearchHovercardController.php on line 37 at [<arcanist>/src/utils/utils.php:37]
See also similar rPa5384ca60470e56a5312d5a7147ddd3ffa2e75d8.
Closes T16075