tag_aliases/index: fix tag category search options excluding empty tags.

Fix Tag.search to not filter out empty tags by default. Set the default
in the tags controller instead.

Fixes various search pages, namely aliases/implications/wiki pages, that
rely on Tag.search and that don't expect it to filter tags out by default.

app/controllers/tags_controller.rb

@@ -9,7 +9,7 @@ class TagsController < ApplicationController
   end
 
   def index
-    @tags = Tag.paginated_search(params)
+    @tags = Tag.paginated_search(params, hide_empty: true)
     @tags = @tags.includes(:consequent_aliases) if request.format.html?
     respond_with(@tags)
   end

app/models/tag.rb

@@ -847,8 +847,8 @@ class Tag < ApplicationRecord
         q = q.name_or_alias_matches(params[:name_or_alias_matches])
       end
 
-      if params[:hide_empty].blank? || params[:hide_empty].to_s.truthy?
-        q = q.where("post_count > 0")
+      if params[:hide_empty].to_s.truthy?
+        q = q.nonempty
       end
 
       if params[:has_wiki].to_s.truthy?