Make envelope sender config work the same way for mail()` as it doe…

…s for SMTP, preferring `Sender` over `sendmail_from` ini setting.

src/PHPMailer.php

@@ -1813,10 +1813,17 @@ protected function mailSend($header, $body)
         //Qmail docs: http://www.qmail.org/man/man8/qmail-inject.html
         //Example problem: https://www.drupal.org/node/1057954
         // CVE-2016-10033, CVE-2016-10045: Don't pass -f if characters will be escaped.
-        if (!empty($this->Sender) && static::validateAddress($this->Sender) && self::isShellSafe($this->Sender)) {
-            $params = sprintf('-f%s', $this->Sender);
+        if ('' === $this->Sender) {
+            $this->Sender = $this->From;
+        }
+        if (empty($this->Sender) && !empty(ini_get('sendmail_from'))) {
+            //PHP config has a sender address we can use
+            $this->Sender = ini_get('sendmail_from');
         }
         if (!empty($this->Sender) && static::validateAddress($this->Sender)) {
+            if (self::isShellSafe($this->Sender)) {
+                $params = sprintf('-f%s', $this->Sender);
+            }
             $old_from = ini_get('sendmail_from');
             ini_set('sendmail_from', $this->Sender);
         }