fix(EMailTemplate): malformed HTML in some cases

when an addBodyListItem() is not directly followed by addBodyButton(), resulting HTML is broken

Signed-off-by: Tomasz Paluszkiewicz <tomasz.paluszkiewicz@gmail.com>

lib/private/Mail/EMailTemplate.php

@@ -436,6 +436,7 @@ EOF;
 		}
 
 		$this->ensureBodyIsOpened();
+		$this->ensureBodyListClosed();
 
 		$this->htmlBody .= vsprintf($this->bodyText, [$text]);
 		if ($plainText !== false) {