Hotfix for desktop crash with missing MPC

libs/builder.lua

@@ -68,7 +68,10 @@ return function(description,opts)
                 if v.draggable then
                     list.buttons = buttons
                 else
-                    table.insert(list,inner_builder(v))
+                    local new_obj = inner_builder(v)
+                    if new_obj then
+                        table.insert(list,new_obj)
+                    end
                 end
             end
             return list
@@ -98,7 +101,10 @@ return function(description,opts)
                     if obj.draggable then
                         list[k].buttons = buttons
                     else
-                        table.insert(list[k],inner_builder(obj))
+                        local new_obj = inner_builder(obj)
+                        if new_obj then
+                            table.insert(list[k],new_obj)
+                        end
                     end
                 end
             end