Take advantage of PHP7+ null-coalescing operator `??` to make code more standard, shorter, and faster instead of custom function with no extra functionality.
Allows code to be better tested and fix two PHPstan errors:
```
------ -----------------------------------------
Line app/Controllers/configureController.php
------ -----------------------------------------
410 Cannot unset offset 'rid' on string.
------ -----------------------------------------
------ ------------------------------------
Line lib/Minz/FrontController.php
------ ------------------------------------
70 Cannot unset offset 'c' on string.
71 Cannot unset offset 'a' on string.
------ ------------------------------------
```
https://github.com/FreshRSS/FreshRSS/issues/4016
a2ab9cf83a