File upload field directory dropdown ordered by id rather than alpha

[robinsowell]

So it's minor but also tends to be irksome. The file upload directory dropdown is ordered by id rather than alpha:

I was going to do a quick fix, but the nested directories made it... not a quick fix, so dropping in here.

Weirdly, on the actual file manager, the top level directories are ordered alpha in the dropdown, but the subcategories are not:

It's on the line between bug and feature, but... it really feels like it shouldn't be ordered that way.