[BUGFIX] Fix broken file reference attachments

This commit fixes FileReference attachments of multiple consequtive mails
that are sent via the mail queue, for example via the forms finisher with
a user and an admin mail, where files need to be attached to both mails.

Classes/Finisher/Forms/FormsFinisher.php

@@ -66,10 +66,6 @@ class FormsFinisher extends AbstractFinisher {
 			return;
 		}
 
-		if ($formRuntime === NULL) {
-			return;
-		}
-
 		$markers = [];
 		$markerLabels = [];
 

Classes/Service/MailTemplateService.php

@@ -895,7 +895,16 @@ class MailTemplateService {
 		$mail->setReplyTo($this->replyToAddress);
 		foreach ($this->markers as $marker) {
 			if ($marker instanceof FileReference) {
-				$mail->addAttachment($marker);
+				$coreFileReferenceMailFile = $this->resourceFactory->createFileReferenceObject(
+					[
+						'uid_local' => $marker->getOriginalResource()->getOriginalFile()->getUid(),
+						'table_local' => 'sys_file',
+						'uid' => uniqid('NEW_MAIL', TRUE)
+					]
+				);
+				$newFileReference = GeneralUtility::makeInstance(FileReference::class);
+				$newFileReference->setOriginalResource($coreFileReferenceMailFile);
+				$mail->addAttachment($newFileReference);
 			}
 		}