kcms/landingpage: hide "Most Used" section when it's empty

(cherry picked from commit 83c84869)

kcms/landingpage/package/contents/ui/main.qml

@@ -203,12 +203,15 @@ KCM.SimpleKCM {
 
         Kirigami.Separator {
             Kirigami.FormData.isSection: true
+            visible: mostUsedGrid.visible
         }
 
         GridLayout {
+            id: mostUsedGrid
             Kirigami.FormData.label: i18n("Most Used Pages:")
             Kirigami.FormData.buddyFor: children[1] // 0 is the Repeater
 
+            visible: recentlyUsedRepeater.count > 0
             Layout.fillWidth: true
             rows: 3
             columns: 2