To reproduce:

- edit any Elisp file, but don't save it;
- open its directory in Dired;
- evaluate `(package-dir-info)'.

Fails with: (file-missing "Opening input file" "No such file or directory"
".../.#blabla.el")

I.e. it tries to open the lock created for the unsaved file as a normal
file and fails. I'm not 100% sure this should be considered a bug, but from
my point of view it is so. Even if this is not a bug, the function should
probably fail with a more descriptive error.

Paul