fix: use array_key_exists() on $_ENV to determine if MariaDB key is set (#26)

Reviewed-on: https://codeberg.org/vlw/scaffold/pulls/26

src/Database/Database.php

@@ -32,10 +32,10 @@
 			?string $host = self::DEFAULT_HOSTNAME,
 			?string $username = self::DEFAULT_USERNAME,
 			?string $password = self::DEFAULT_PASSWORD,
-			string $database
+			?string $database = ""
 		) {
 			// Create key if it does not exist
-			if (!$_ENV["mariadb"]) {
+			if (!array_key_exists("mariadb", $_ENV)) {
 				$_ENV["mariadb"] = [];
 			}