FIX: Query syntax error in UserBadge.update_featured_ranks! (#30979)

This commit fixes an SQL syntax error in
`UserBadge.update_featured_ranks!` when
the `user_ids` param is an empty array `[]`.

This was causing the `Jobs::BackfillBadge` job to raise the following
exceptions:

```
Job exception: ERROR:  syntax error at or near ")"
LINE 6:   AND user_id IN ()
```

This commit fixes the same error in
`UserState.update_distinct_badge_count` as well

Follow-up to 3e4eac0fed05daedcdea50d6275e143469d55eda

spec/models/user_stat_spec.rb

@@ -215,7 +215,7 @@ RSpec.describe UserStat do
     end
   end
 
-  describe "update_distinct_badge_count" do
+  describe ".update_distinct_badge_count" do
     fab!(:user)
     let(:stat) { user.user_stat }
     fab!(:badge1) { Fabricate(:badge) }