Better handle sitatuations where a user's role on a team is undefined

[stevegrunwell]

In some situations (especially when testing using database factories), the "role" column on the team_user table may be left NULL. As a result, attempting to check the user's permissions based on their role causes an error, as Jetstream::findRole() requires a string.

For example:

use App\Models\Team;
use App\Models\User;

$team = Team::factory()
	->with(User::factory())
	->create();

$team->users->first()->hasTeamPermission($team, 'read');
#=> TypeError: Laravel\Jetstream\Jetstream::findRole(): Argument #1 ($key) must be of type string, null given, called in /vendor/laravel/jetstream/src/HasTeams.php on line 145

This PR ensures that Jetstream::findRole() is only called if we have a corresponding role, preventing this error. Similarly, teamPermissions() will no longer cause a "ErrorException: Attempt to read property "permissions" on null" exception when the role is undefined.

[driesvints]

Seems to breaks the test suite. Please mark this PR as ready for review when they're passing again.

[stevegrunwell]

Will do, I'm working through the pipeline to figure out why the autoloader isn't getting updated 🤔

[stevegrunwell]

@driesvints figured it out: I had the following in composer.json:

"autoload-dev": {
    "psr-4": {
        // ...
        "Database\\": "database/"
    }
},

On a case-insensitive filesystem (like macOS) it wasn't a big deal, but PSR-4 would expect to find Database\Factories\TeamFactory in database/Factories/TeamFactory.php (capital "F"). PSR-4 failure on my part 😬