Only chop off leading @ from tokenized license text if needed
requested to merge ngraham/discover:dont-unconditionally-chop-off-the-first-character-from-unknown-license-text into master
Apparently at some point in the past, tokenized non-SPDX license labels got prefixed with "@". As a result, the code unconditionally chopped off the first character.
At some point, tokenizing stopped always doing that, causing some license labels to be shown with their first letter missing.
I don't know if the prepending might come back in the future, so to be safe, let's only conditionally remove the first character if it's "@".
Testable with plasma-discover appstream://dwarffortress.desktop
BUG: 491172 FIXED-IN: 6.1.4