[FIX] Fallback content-type as application/octet-stream for FileSystem uploads (#16776)

app/file-upload/server/config/FileSystem.js

@@ -21,7 +21,7 @@ const FileSystemUploads = new FileUploadClass({
 				file = FileUpload.addExtensionTo(file);
 				res.setHeader('Content-Disposition', `attachment; filename*=UTF-8''${ encodeURIComponent(file.name) }`);
 				res.setHeader('Last-Modified', file.uploadedAt.toUTCString());
-				res.setHeader('Content-Type', file.type);
+				res.setHeader('Content-Type', file.type || 'application/octet-stream');
 				res.setHeader('Content-Length', file.size);
 
 				this.store.getReadStream(file._id, file).pipe(res);