Fix load-more button state

modules/webapp/src/main/elm/Data/Items.elm

@@ -10,7 +10,9 @@ module Data.Items exposing
     , first
     , flatten
     , idSet
+    , isEmpty
     , length
+    , nonEmpty
     , replaceIn
     , unwrapGroups
     )
@@ -23,6 +25,16 @@ import Set exposing (Set)
 import Util.List
 
 
+isEmpty : ItemLightList -> Bool
+isEmpty list =
+    List.all (.items >> List.isEmpty) list.groups
+
+
+nonEmpty : ItemLightList -> Bool
+nonEmpty list =
+    not (isEmpty list)
+
+
 flatten : ItemLightList -> List ItemLight
 flatten list =
     List.concatMap .items list.groups