fix: wsod on attach shares when not enough shares available at date

src/Entity/ShareTransaction.php

@@ -734,6 +734,9 @@ class ShareTransaction extends ContentEntityBase implements ShareTransactionInte
       }
       else {
         $share_ids = array_values($this->getShareholder()->getCurrentShareIdsAtDate($date));
+        if (count($share_ids) < abs($this->getQuantity())) {
+          throw new ShareholderRegisterMissingSharesException();
+        }
         for ($i = 0; $i < abs($this->getQuantity()); $i++) {
           $share = Share::load($share_ids[$i]);
           $share->get('share_transaction_ids')->appendItem($this->id());