If F4 is pressed to try to edit a remote folder, then an empty file is edited, and an error message is shown. This proposal is aimed to solve that.
Notes: This also happened before applying https://phabricator.kde.org/D27258 //("Manage what happens when a PanelViewerBase (e.g. using Shift+F3) tries to open a nonexistent local file")// or applying https://phabricator.kde.org/D27259 //("Manage the use of Shift+F4 when opening a local file that exists, or a remote folder or remote file that exists")// though some of the code that was introduced in https://phabricator.kde.org/D27259 was reused in the present code review.