FIX: improves tag-list setting (#9574)

- Prevents setting to display an empty tag
- Updates dropdown when selecting/removing tag

app/assets/javascripts/admin/components/site-settings/tag-list.js

@@ -1,15 +1,17 @@
 import discourseComputed from "discourse-common/utils/decorators";
 import Component from "@ember/component";
+import { action } from "@ember/object";
 
 export default Component.extend({
   @discourseComputed("value")
   selectedTags: {
     get(value) {
-      return value.split("|");
-    },
-    set(value) {
-      this.set("value", value.join("|"));
-      return value;
+      return value.split("|").filter(Boolean);
     }
+  },
+
+  @action
+  changeSelectedTags(tags) {
+    this.set("value", tags.join("|"));
   }
 });