Errors raised in DB_storage::toString() if there are multi-column keys, on PHP >= 7

[MarkMaldaba]

As reported by PHPCompatibility:

FILE: ./DB/storage.php
-----------------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
-----------------------------------------------------------------------------
 254 | ERROR | Indirect access to variables, properties and methods will be
     |       | evaluated strictly in left-to-right order since PHP 7.0. Use
     |       | curly braces to remove ambiguity.
-----------------------------------------------------------------------------

On PHP 5 this code correctly retrieves the class property whose name is held in $keyname[$i].

As of PHP 7 it raises a number of PHP errors. They are notices on PHP 7 and warnings on PHP 8:

Warning: Array to string conversion in DB/storage.php on line 254

Warning: Undefined property: DB_storage::$Array in DB/storage.php on line 254

Warning: Trying to access array offset on null in DB/storage.php on line 254

Adding explicit braces resolves this issue and restores the intended behaviour across all PHP versions.