fix(dispatcher): skip undefined components in collectComponents (#2404)

layout.footer (and other optional layout slots) can be undefined
when disabled. Adding undefined to the seen Set caused a crash in
componentResources.ts when destructuring component properties.

quartz/plugins/pageTypes/dispatcher.ts

@@ -55,7 +55,7 @@ function collectComponents(
       layout.footer,
     ]
     for (const c of all) {
-      seen.add(c)
+      if (c) seen.add(c)
     }
   }
   return [...seen]