Revert "DEV: make pre-initializer a bit safer"

This reverts commit 029a26733a.

This whole experiment is too unstable

assets/javascripts/discourse-assign/pre-initializers/extend-category-for-assign.js.es6

@@ -11,11 +11,6 @@ export default {
         "custom_fields.enable_unassigned_filter",
         {
           get(fieldName) {
-            // not sure how this is possible but appears to happen in some cases
-            // in test
-            if (!this && !this.custom_fields) {
-              return false;
-            }
             return Ember.get(this.custom_fields, fieldName) === "true";
           }
         }