Steps to reproduce the issue

Trigger an error while uploading an extension that results in $package not being an array (setting a small upload file size should do the trick).

Expected result

Uninstall is aborted gracefully in error conditions.

Actual result

Uninstall is aborted with a PHP Notice (which depending on the day of the week may qualify as a FPD security issue): Trying to access array offset on value of type bool in administrator/components/com_installer/models/install.php on line 178.

System information (as much as possible)

Joomla 3.9.19, PHP 7.4, all other information irrelevant

Additional comments

The line triggering the notice should only be triggered when $package is an array, as the requisite data is not available when $package is of any other data type (this would be a great use case for a DTO defining the list of allowed properties and an object|null type on the $package, but I won't push my luck here ? ).