dired-subtree-insert doesn't work when cursor on '.' or '..' (with fix)

[notuntoward]

On line 489 of dired-subtree.el, the code:

(let* ((dir-name (dired-get-filename nil))

should be:

(let* ((dir-name (dired-get-filename nil t))

If 't' is included in the arguments of dired-get-filename then dired-subtree-insert works when the cursor is on '.' or '..'. Without the 't', it errors out.

The call to dired-get-filename is correct elsewhere.