Cover Art Fetcher: allow applying just the found cover

[ronso0]

... + some layouts tweaks

before:

this PR:

Closes #11086

[Swiftb0y]

The status message seems clunky, couldn't that be conveyed better by greying out the apply button when its not possible to apply and then updating the "current cover art" preview if it was successfully applied?

[ronso0]

greying out the apply button when its not possible to apply and then updating the "current cover art" preview if it was successfully applied?

Thank you, that slipped through. IIRC I already fixed that in #11112, I'll look into either backporting the fix or do it manually in DlgTagFetcher.

[ronso0]

Actually, the 'Current Cover' should be updated after it was written to the track file succesfully (need to click Okay to overwrite the track file).
The status message is displayed already when the file overwrite dialog pops up.

[ronso0]

Furthermore, there are some inconsistencies in the file update process: the tags are written directly whereas the cover art update is initiated but results (dialog/success/failure) are processed via signals/slots, so there's no guarantee the messages are displayed in the correct order.

• "Selected metadata applied" message may be displayed after the cover was written
• "Metadata & Cover Art applied" is displayed by slotWorkerCoverArtUpdated even though that slot is responsible only for the cover art (until now, it was assumed that both tags and cover are updated simultaneously).

I'll check whether that can be fixed while keeping the tr strings in place.

[Swiftb0y]

LGTM. Thank you.

[ronso0]

Thanks for your review!

Furthermore, there are some inconsistencies in the file update process: the tags are written directly whereas the cover art update is initiated but results (dialog/success/failure) are processed via signals/slots, so there's no guarantee the messages are displayed in the correct order.

* "Selected metadata applied" message may be displayed after the cover was written

* "Metadata & Cover Art applied" is displayed by `slotWorkerCoverArtUpdated` even though that slot is responsible only for the cover art (until now, it was assumed that both tags and cover are updated simultaneously).

Follow-up is #12041