fix uploads with no extensions

src/controllers/uploads.js

@@ -185,6 +185,9 @@ function uploadFile(uid, uploadedFile, callback) {
 	if (meta.config.hasOwnProperty('allowedFileExtensions')) {
 		var allowed = file.allowedExtensions();
 		var extension = path.extname(uploadedFile.name);
+		if (!extension) {
+			extension = '.' + mime.extension(uploadedFile.type);
+		}
 		if (allowed.length > 0 && allowed.indexOf(extension) === -1) {
 			return callback(new Error('[[error:invalid-file-type, ' + allowed.join(', ') + ']]'));
 		}