[imp] Drag and Drop attachment and logout with expired session

[Luis Felipe Marzagao]

Hello:

When I drag and drop a file to "Add Attachment" I get logged out of 
horde with the msg:

"Your session has expired. Please login again."

If I add the attachment by clicking on "Add Attachment", then it works.

Horde 5.1.2
IMP 6.1.3

I tried on Firefox and Chrome. Same behavior.

Thanks.
Luis Felipe