Merge pull request #150 from bbassie:patch-1

Fix Issue #149

expcore/gui/prototype.lua

@@ -349,6 +349,7 @@ local function event_handler_factory(event_name)
         local element = event.element
         if not element or not element.valid then return end
         local element_define = Gui.defines[element.name]
+        if not element_define then return end
         element_define:raise_custom_event(event)
     end)
 
@@ -411,4 +412,4 @@ Gui._prototype_element.on_text_changed = event_handler_factory(defines.events.on
 Gui._prototype_element.on_value_changed = event_handler_factory(defines.events.on_gui_value_changed)
 
 -- Module return
-return Gui
+return Gui