fix some ui bug about draft release (#15137)

* fix some ui bug about draft release

- should not show draft release in tag list because
  it will't create real tag
- still show draft release without tag and commit message
  for draft release instead of 404 error
- remove tag load for attachement links because it's useless

Signed-off-by: a1012112796 <1012112796@qq.com>

* add test code

* fix test

That's because has added a new release in relaese test database.

* fix dropdown link for draft release

models/fixtures/release.yml

@@ -43,3 +43,15 @@
   is_tag: true
   created_unix: 946684800
 
+-
+  id: 4
+  repo_id: 1
+  publisher_id: 2
+  tag_name: "draft-release"
+  lower_tag_name: "draft-release"
+  target: "master"
+  title: "draft-release"
+  is_draft: true
+  is_prerelease: false
+  is_tag: false
+  created_unix: 1619524806