[Patch] JosmAction.checkAndConfirmOutlyingOperation() should also handle dataset without download area

[GerdP]

We have some actions (unglue, delete, join area) which call this method to ask for user confirmation with texts like

"You are about to delete nodes outside of the area you have downloaded."

This message doesn't cover the case that the user didn't donwload any area when e.g. an overpass query was used or download object.
I think the text should be changed to

"You are about to delete nodes not inside any area you have downloaded."

and the test should be changed to detect the corresponding case.