not uploading empty directories

[johrstrom]

When working through #3663 I've found that uploading empty directories does not work at all, at least in 3.1.x and in the current development branch (4.0).

I don't know when this stopped working, but it seems like when we fix this bug we should additionally add a test case for the same.

To replicate simply make a directory that has a file and an empty directory. When you upload this directory - only the file is uploaded. The empty directory was not created.