coverView - deselect cover after editting albumORartist fields
it avoids picking up (pressing ENTER key) a cover selected from an old search
txt fields - using the signal textChanged() instead of editingfinished()
the signal editingfinished is emitted only after focus loss and it is bad when the user press ENTER without release the field.
DlgCoverArtFetcher::slotApply - it ensures that the current item is not NULL and is selected (before try changing cover)