[Translator] Fix Empty translations with Qt files

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | n/a
| Fixed tickets | no
| License       | MIT
| Doc PR        |  

When you use ts files, QtLinguist, generate empty string for all translations, even if there are not translated yet.

It could be a good idea to generate an entry in the MessageCatalogue only if translation value is not empty.