Removed bug that allows duplicate entries per donation in the thankyou_a_b table

Signed-off-by: Edouard Poitras <edouard@eclipse.org>

thankyou.php

diff --git a/thankyou.php b/thankyou.php
index cf57554..a8e6157 100644
--- a/thankyou.php
+++ b/thankyou.php
@@ -76,8 +76,11 @@
     $data = $paypal->get_transaction_data();
     $amount = $app->sqlSanitize($data['amount']);
     $test = $app->sqlSanitize($_GET['cm']);
-    if (is_numeric($amount)) {
-      $sql = "INSERT INTO thankyou_a_b VALUES (NOW(), '$test', $amount)";
+    $transaction_id = $data['transaction_id'];
+    $sql = "SELECT * FROM thankyou_a_b WHERE transaction_id = '$transaction_id'";
+    $res = $app->eclipse_sql($sql);
+    if (is_numeric($amount) && mysql_num_rows($res) === 0) {
+      $sql = "INSERT INTO thankyou_a_b VALUES (NOW(), '$test', $amount, '$transaction_id')";
       $app->eclipse_sql($sql);
     }
   }