AVideo Vulnerable to Wallet Balance Double-Spend via TOCTOU Race Condition in transferBalance

WWBN AVideo is an open source video platform. In versions up to and including 26.0, the `transferBalance()` method in `plugin/YPTWallet/YPTWallet.php` contains a Time-of-Check-Time-of-Use (TOCTOU) race condition. The method reads the sender's wallet balance, checks sufficiency in PHP, then writes the new balance — all without database transactions or row-level locking. An attacker with multiple authenticated sessions can send concurrent transfer requests that all read the same stale balance, each passing the balance check independently, resulting in only one deduction being applied while the recipient is credited multiple times. Commit 34132ad5159784bfc7ba0d7634bb5c79b769202d contains a fix.