fix: $routes->group('/', ...) creates the route foo///bar

[kenjis]

Description

$routes->group('admin', static function ($routes) {
    $routes->group('/', static function ($routes) {
        $routes->get('list', 'Admin\Users::list');
    });
});

creates

+--------+--------------+------------------------------------------+----------------+---------------+
| Method | Route        | Handler                                  | Before Filters | After Filters |
+--------+--------------+------------------------------------------+----------------+---------------+
| GET    | admin///list | \App\Controllers\Admin\Users::list       |                | toolbar       |
+--------+--------------+------------------------------------------+----------------+---------------+

This PR fixes the route:

+--------+------------+------------------------------------------+----------------+---------------+
| Method | Route      | Handler                                  | Before Filters | After Filters |
+--------+------------+------------------------------------------+----------------+---------------+
| GET    | admin/list | \App\Controllers\Admin\Users::list       |                | toolbar       |
+--------+------------+------------------------------------------+----------------+---------------+

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[MGatner]

Can you add tests for the following please?

1. Group '/', subgroup ''
2. Group '', subgroup ''
3. Group '', subgroup '/'

[kenjis]

Added tests.

[MGatner]

Thank you. Looks good pending test results.

[sfadschm]

I think the "so it" can be removed the way the previous line is phrased.

[kenjis]

@sfadschm Oh, thanks! I didn't understand the sentence.