DlgCoverArtFullSize won't close if no cover was found

[ronso0]

Bug Description

occurs with DlgCoverArtFullSize initialized from WCoverArtLabel in DlgTrackInfo

• open Track Properties for a track with no cover
• WCoverArtLabel shows default cover
• click default cover
• minimal DlgCoverArtFullSize with no cover is shown
• clicking close button or inside the empyt cover area does nothing (actually it triggers DlgCoverArtFullSize::slotLoadTrack(nullptr) for some reason..)
• only closing the parent DlgTrackInfo will close the cover window

Version

2.3.3 and 2.4-alpha

OS

Ubuntu Studio 20.04 / X11 / xfce 4.14 / Qt 5.12.8

[ronso0]

Issue seems to be that close() in DlgCoverArtFullSize::slotCoverFound does nothing.

IMO to fix this sustainably a bigger refactoring is required, it just doesn't make sense to me that the dialog is opened and then closed again if no cover is found.
DlgCoverArtFullSize shouldn't be opened in the first place if no cover is found, similiar to how it's done in WCoverArt::mouseReleaseEvent

[ronso0]

or maybe #11022 is sufficient