lock_commission_unless_purchased.php

<?php

function affwp_edd_block_commission_unless_purchased( $referral_amount, $affiliate_id, $amount, $reference, $product_id ) {

    // get referring affiliate ID
    $affiliate_id = affiliate_wp()->tracking->get_affiliate_id();

    // get user ID of referring affiliate
    $user_id = affwp_get_affiliate_user_id( $affiliate_id );

    if ( ! ( function_exists( 'edd_has_user_purchased' ) && edd_has_user_purchased( $user_id, array( $product_id ) ) ) ) {
        $referral_amount = 0.00;
    }

    return $referral_amount;

}
add_filter( 'affwp_calc_referral_amount', 'affwp_edd_block_commission_unless_purchased', 10, 5 );

very nice!