KVPage: fix crash from empty page due to item deletion (#9974)

Fixes #9972.

frontend/ui/widget/keyvaluepage.lua

@@ -608,6 +608,7 @@ function KeyValuePage:_populateItems()
     -- first we check if no unfit item at all
     local width_ratio
     if (#self.kv_pairs == 0) or
+        (#key_widths == 0) or
         (key_widths[#key_widths] <= key_w and value_widths[#value_widths] <= value_w) then
         width_ratio = 1/2
     end
@@ -747,6 +748,8 @@ end
 function KeyValuePage:removeKeyValueItem(kv_item)
     if kv_item.kv_pairs_idx then
         table.remove(self.kv_pairs, kv_item.kv_pairs_idx)
+        self.pages = math.ceil(#self.kv_pairs / self.items_per_page)
+        self.show_page = math.min(self.show_page, self.pages)
         self:_populateItems()
     end
 end