[Tags] Fix category for non-existant tags

Regressed in 4cd32c5f87
Caching nil as a category can cause problems in a bunch of places

app/models/pool.rb

@@ -129,7 +129,7 @@ class Pool < ApplicationRecord
     if name =~ /\A\d+\z/
       name.to_i
     else
-      Pool.where("lower(name) = ?", name.downcase.tr(" ", "_")).pick(:id)
+      Pool.where("lower(name) = ?", name.downcase.tr(" ", "_")).pick(:id).to_i
     end
   end
 

app/models/post_set.rb

@@ -42,7 +42,7 @@ class PostSet < ApplicationRecord
     if name =~ /\A\d+\z/
       name.to_i
     else
-      PostSet.where("lower(shortname) = ?", name.downcase.tr(" ", "_")).pick(:id)
+      PostSet.where("lower(shortname) = ?", name.downcase.tr(" ", "_")).pick(:id).to_i
     end
   end
 

app/models/tag.rb

@@ -119,7 +119,7 @@ class Tag < ApplicationRecord
 
       def category_for(tag_name)
         Cache.fetch("tc:#{tag_name}") do
-          Tag.where(name: tag_name).pick(:category)
+          Tag.where(name: tag_name).pick(:category).to_i
         end
       end
 

test/unit/tag_test.rb

@@ -17,6 +17,10 @@ class TagTest < ActiveSupport::TestCase
       assert_equal(Tag.categories.artist, Tag.category_for("!@ab"))
     end
 
+    should "return general for a tag that doesn't exist" do
+      assert_equal(Tag.categories.general, Tag.category_for("missing"))
+    end
+
     should "fetch for multiple tags" do
       create(:artist_tag, name: "aaa")
       create(:copyright_tag, name: "bbb")