[Mime] Fixed `Mime\Message::ensureValidity()` when a required header is set, but has an empty body#57065

fabpot merged 1 commit intosymfony:5.4symfony/symfony:5.4from

rhertogh:mime_message_ensure_validity_with_empty_headerrhertogh/symfony-symfony:mime_message_ensure_validity_with_empty_headerCopy head branch name to clipboard