Email error (smtp error) when non ASCII character in the display_name, no mail sent

We have occassional problems with the extension, that we get the error

Validation failed for:...

This causes failure of sending the mail. Looks like a SMTP error, but in truth it is thrown before by civicrm/vendor/pear/mail/Mail/RFC822.php

As a quick workaround, I deleted $display_name in line 442 of invoicehelper-master/CRM/Invoicehelper/Contribute/Form/Task/Invoice.php

But maybe there is a better solution for that.