don't use BCC for single-recipient email

Author: simonLeary42

resources/lib/UnityMailer.php

@@ -113,7 +113,7 @@ public function sendMail(string $recipients, ?string $template = null, mixed $da
                         $this->addBCC($addr);
                     }
                 } else {
-                    $this->addBCC($recipients);
+                    $this->AddAddress($recipients);
                 }
             }
         }