Fix all interstellar construction turrets being invalidated by GC

Author: Quezler

mods/se-interstellar-construction-requests-fulfillment/info.json

@@ -2,7 +2,7 @@
     "name": "se-interstellar-construction-requests-fulfillment",
     "title": "Space Exploration - interstellar construction requests fulfillment",
     "description": "Keeping building equipment stocked at every planet is tedious, just shoot it there from nauvis.",
-    "version": "1.0.1",
+    "version": "1.0.2",
     "author": "Quezler",
     "factorio_version": "1.1",
     "dependencies": [

mods/se-interstellar-construction-requests-fulfillment/scripts/handler.lua

@@ -210,7 +210,7 @@ end
 
 function Handler.gc(event)
   for unit_number, struct in pairs(global.structs) do
-    if not struct.valid then
+    if not struct.entity.valid then
       log('garbage collected struct #' .. unit_number)
       global.structs[unit_number] = nil
     end