minor #6419 Update routing.rst (tamtamchik)

This PR was submitted for the 3.0 branch but it was merged into the 2.3 branch instead (closes #6419).

Discussion
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Update routing.rst

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | none

The described version of the file was breaking "default value" functionality, and if user would access this page without `name` variable it'll get warning:

 `Notice: Undefined variable: name in ../src/pages/hello.php on line 2`

Commits
-------

a29a319 Update routing.rst

Author: xabbuh

create_framework/routing.rst

@@ -33,7 +33,7 @@ As we now extract the request query parameters, simplify the ``hello.php``
 template as follows::
 
     <!-- example.com/src/pages/hello.php -->
-    Hello <?php echo htmlspecialchars($name, ENT_QUOTES, 'UTF-8') ?>
+    Hello <?php echo htmlspecialchars(isset($name) ? $name : 'World', ENT_QUOTES, 'UTF-8') ?>
 
 Now, we are in good shape to add new features.