#1525 Assertion when deleting a directory containing DISAPPEARED files

[LETARTARE]

In a project, if I want to delete an ‘adding’ directory and all its files, I use the context menu on this directory ‘Remove adding/*’.
If the directory and these files have disappeared from the disk => 'CB' crashes

I propose a fix that avoids this crash and offers the solution to unregister the files from the project ('Remove files..').

This problem has existed for a very long time, but I hadn't taken the time to try and solve it.

Tested on ‘Leap-15.6’ only.
Attachments: assertion and fix

[Miguel Gimenez]

Applied in [r13650], thank you.

I had to replace tabs with spaces and UTF-8 quotes with single quotes.