No error message shown when trying to save read-only files

[fernandreu]

When saving a read-only file, the tool does not give any error message, but the file is not saved either.

In debug mode, it does give an error message:

This should be properly captured and shown in both configurations instead.

Note: this is not as much of an issue when using the Save As option because the save file dialog already does a read-only (and write permission) check.