bug#52004: dired-rename-subdir-2: Expected to find ‘/tmp/a/./’ in headerline of /tmp/a/

[積丹尼 Dan Jacobson]

$ mkdir /tmp/a /tmp/b
$ emacs -Q /tmp/a
Put the cursor on the "." line, and hit R and try and move it to /tmp/b .
Overwrite ‘/tmp/b’? [Type yn!q or C-h] y
dired-rename-subdir-2: Expected to find ‘/tmp/a/./’ in headerline of /tmp/a/

Yes, on /tmp we can move /tmp/a to /tmp/b (creating /tmp/a/b/) easily.

But still, the above problem should be detected earlier, before the
question is shown to the user.

emacs-version "27.1"