FIX: track mutations on topic edit category-chooser only on select (#7528)

FIX: track mutations on topic edit category-chooser only on select (#7528)

diff --git a/app/assets/javascripts/discourse/templates/topic.hbs b/app/assets/javascripts/discourse/templates/topic.hbs
index 1a4f1e0..48bd3d0 100644
--- a/app/assets/javascripts/discourse/templates/topic.hbs
+++ b/app/assets/javascripts/discourse/templates/topic.hbs
@@ -22,7 +22,10 @@
           {{/if}}
             {{text-field id="edit-title" value=buffered.title maxlength=siteSettings.max_topic_title_length autofocus="true"}}
             {{#if showCategoryChooser}}
-              {{category-chooser class="small" value=buffered.category_id}}
+              {{category-chooser
+                class="small"
+                value=(unbound buffered.category_id)
+                onSelect=(action (mut buffered.category_id))}}
             {{/if}}
 
             {{#if canEditTags}}

GitHub sha: 9b75320d