Fix error when payment methods have been deleted

[sreichel]

Fixed Issues (if relevant)

1. Fixes Bug: Fatal error in salesOrderBeforeSave event for deleted payment #280

Manual testing scenarios (*)

1. delete payment method that is used for existing orders
2. go to admin orders

Questions or comments

Related code: (can return false)

    /**
     * Retrieve order payment model object
     *
     * @return Mage_Sales_Model_Order_Payment|false
     */
    public function getPayment()
    {
        foreach ($this->getPaymentsCollection() as $payment) {
            if (!$payment->isDeleted()) {
                return $payment;
            }
        }
        return false;
    }

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[github-actions]

Unit Test Results

1 files  ±0  1 suites  ±0   0s ⏱️ ±0s
0 tests ±0  0 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
7 runs  ±0  5 ✔️ ±0  2 💤 ±0  0 ❌ ±0 

Results for commit f835cb6. ± Comparison against base commit 2e5b42e.