Not Supported Document Types #48

Hi,

First of all, congrats for your great job, viewer.js is a very usefull tool.

Just one question: is it possible, when you try to open an unsupported document type (xlsx, docx, etc) that viewer.js shows a message like "The document you are trying to visualize is not supported, you can download it here"?

Actually, when I try to view an unsupported filetype, the viewer just stay blank, and the download link on the upper right corner doesn't works...

Thanks !!!