Fixed drive switching on windows

[mbwilding]

Proposed fix for the traversal part of issue #326

[mbwilding]

I am currently looking into how to fix browsing network mapped drives.

EDIT1: turns out we can traverse mapped drives, but still finding the right place to apply the fix.
EDIT2: Sorted out mapped/network drives

[stevearc]

Couple questions

[mbwilding]

All the tests are passing on my fork now.
I put that addslash back in but added a check for \\ in that function instead.

EDIT: Just saw your other comment, fixing that now.

[mbwilding]

I tried the early return, but it needs the logic below that does checks like if it is a directory or not then adjusts the path. It just throws buffer errors otherwise.

Top section just handles the drive select logic.

[stevearc]

I'm surprised by the presence of backslashes in certain locations. I'm going to need to pull this locally and poke around a bit, but I don't have a windows machine with me at the moment. Will follow up on this next week.

[stevearc]

@mbwilding okay, I think I have a better fix for the double \\ when opening oil with nvim .. LMK what you think

[mbwilding]

@stevearc Your changes work as expected, I like it.
Tested mapped drives and local, as well as nvim .
LGTM.