Fix setPaymentAmount storing amount when condition is inverted

Author: lukeholder

src/elements/Order.php

@@ -2459,7 +2459,7 @@ public function setPaymentAmount(float $amount): void
         $paymentCurrency = Plugin::getInstance()->getPaymentCurrencies()->getPaymentCurrencyByIso($this->getPaymentCurrency());
         $amount = Currency::round($amount, $paymentCurrency);
 
-        if ($amount <= 0) {
+        if ($amount > 0) {
             $this->_paymentAmount = $amount;
         }
     }