Do not mark a row imported once its listing is gone

The last write is followed by a pause, and an empty remote playlist
never reaches a check at all, so the list could be replaced before the
import reported itself finished. Marking it then attached to whichever
row carries that ID now — on another account, a different playlist
shown as already imported.

Clearing the in-progress state stays unconditional: it describes a row
that is no longer there either way.

Yattee/Views/Settings/ImportPlaylistsView.swift

@@ -474,10 +474,18 @@ struct ImportPlaylistsView: View {
             }
 
             await MainActor.run {
-                importedPlaylistIDs.insert(playlist.id.playlistID)
                 importingPlaylistID = nil
                 importProgress = nil
 
+                // The list can be replaced after the last video is written —
+                // an empty remote playlist never reaches a check at all.
+                // Marking it imported would attach to whatever row carries
+                // that ID now, which on another account is a different
+                // playlist.
+                guard generation == listGeneration else { return }
+
+                importedPlaylistIDs.insert(playlist.id.playlistID)
+
                 if skippedCount > 0 {
                     appEnvironment.toastManager.showSuccess(
                         String(localized: "import.playlists.added.title"),