Rescue when there's no extension in the remotable (#6358)

* Rescue when there's no extension in the remotable
Sometimes the remotable is pointing to a directory with no file
extension. Maybe it should not be expecting to identify based on
extensions to begin with, but since it's the case, it should be ready
for it.

* Fix codeclimate issue

* Check if filename is nil instead of rescueing exception
Suggestion made in the PR

* Avoid concatenation issue if filename is nil
If filename is nil, extname was undefined

* Invert condition
Address PR comments