Restore is always considered successful if no error occurs

[jamesrb1]

If a user restores purchases, but no purchases are available to be restored, the completed callback does not get called. This fixes the issue.

[vegaro]

I’ve also found confusing in the past the fact that the callback is not notified if nothing is restored, so I am happy that is changing. FWIW, this PR is the one that changed it intentionally #3233 and I think the original idea, of not not displaying “Purchases restored successfully” is good, but the side effect of not notifying the callback is more confusing in my opinion than displaying the dialog.

I agree with your points of looking for a better solution for this, which would be displaying a dialog that says "Nothing was restored" and calling the callback feels like the proper solution.