FIX: when creating a topic in a category that only allows tags from a tag group, don't allow creation of new tags

lib/discourse_tagging.rb

@@ -40,7 +40,7 @@ module DiscourseTagging
           selected_tags: tag_names
         ).to_a
 
-        if tags.size < tag_names.size && (category.nil? || category.tags.count == 0)
+        if tags.size < tag_names.size && (category.nil? || (category.tags.count == 0 && category.tag_groups.count == 0))
           tag_names.each do |name|
             unless Tag.where(name: name).exists?
               tags << Tag.create(name: name)

spec/integration/category_tag_spec.rb

@@ -100,6 +100,13 @@ describe "category tag restrictions" do
       expect(filter_allowed_tags(for_input: true)).to contain_exactly(tag3)
       expect(filter_allowed_tags(for_input: true, category: other_category)).to contain_exactly(tag3)
     end
+
+    it "enforces restrictions when creating a topic" do
+      category.allowed_tag_groups = [tag_group1.name]
+      category.reload
+      post = create_post(category: category, tags: [tag1.name, "newtag"])
+      expect(post.topic.tags.map(&:name)).to eq([tag1.name])
+    end
   end
 
   context "tag groups with parent tag" do