Merge pull request #1691 from nextcloud/backport/1689/stable21

[stable21] Use text/plain as content type for fetching the document

Author: juliusknorr

lib/Service/ApiService.php

@@ -114,7 +114,7 @@ public function fetch($documentId, $sessionId, $sessionToken) {
 			} catch (NotFoundException $e) {
 				return new NotFoundResponse();
 			}
-			return new FileDisplayResponse($file);
+			return new FileDisplayResponse($file, 200, ['Content-Type' => 'text/plain']);
 		}
 		return new NotFoundResponse();
 	}