Shutup LinkPreviewDelegate

Make sure that the console isn't spammed having `linkpreviewer` undefined in `LinkPreviewDelegate`, even though it shouldn't ever be and I couldn't find any case where it was but my console was still intermittently getting spammed.

src/qml/Component/Timeline/MessageDelegate.qml

@@ -68,7 +68,7 @@ TimelineContainer {
         }
         LinkPreviewDelegate {
             Layout.fillWidth: true
-            active: !currentRoom.usesEncryption && currentRoom.urlPreviewEnabled && Config.showLinkPreview && root.showLinkPreview
+            active: !currentRoom.usesEncryption && currentRoom.urlPreviewEnabled && Config.showLinkPreview && root.showLinkPreview && !root.linkPreview.empty
             linkPreviewer: root.linkPreview
             indicatorEnabled: root.isVisibleInTimeline()
         }