empty tag results in double underscore in filename

[tgruene]

branch: main, date of testing: 12/5/2025
when the TAG field is empty, the resulting filename includes two underscode '__'. Personally, I find this unpleasing. A simple
if TAG not None: filename_pattern += f'_{TAG}'
would do, wouldn't it?

[kferjaoui]

This is not a bug, just how the filename is constructed in the epoc-utils.
PR#epoc-ed/epoc-utils#14 should remedy the issue (commit c93dc92)