Fix issue with filenames with plupload 2.1.2

With m0xie v1.2.1 and plupload 2.1.2 the filename from
fileUpload.FileName comes through as "blob" and this causes the
extension check to fail.
![blobfilename](https://cloud.githubusercontent.com/assets/78284/3697958/46fa9228-13b5-11e4-98b5-6f66fd7d4759.JPG)