bug symfony#57228 [Mime] fix PHP 7 compatibility (xabbuh)

This PR was merged into the 5.4 branch.

Discussion
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[Mime] fix PHP 7 compatibility

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | following symfony#57065
| License       | MIT

Commits
-------

c5c6f08 fix PHP 7 compatibility

Author: fabpot

src/Symfony/Component/Mime/Message.php

@@ -124,11 +124,18 @@ public function toIterable(): iterable
 
     public function ensureValidity()
     {
-        if (!$this->headers->get('To')?->getBody() && !$this->headers->get('Cc')?->getBody() && !$this->headers->get('Bcc')?->getBody()) {
+        $to = (null !== $header = $this->headers->get('To')) ? $header->getBody() : null;
+        $cc = (null !== $header = $this->headers->get('Cc')) ? $header->getBody() : null;
+        $bcc = (null !== $header = $this->headers->get('Bcc')) ? $header->getBody() : null;
+
+        if (!$to && !$cc && !$bcc) {
             throw new LogicException('An email must have a "To", "Cc", or "Bcc" header.');
         }
 
-        if (!$this->headers->get('From')?->getBody() && !$this->headers->get('Sender')?->getBody()) {
+        $from = (null !== $header = $this->headers->get('From')) ? $header->getBody() : null;
+        $sender = (null !== $header = $this->headers->get('Sender')) ? $header->getBody() : null;
+
+        if (!$from && !$sender) {
             throw new LogicException('An email must have a "From" or a "Sender" header.');
         }