modqueue: optimize sql queries.

* Include appeals and flags.
* Avoid an existence query for pools.
* Avoid a query checking if the user has previously approved the post.
  This is a rare condition and it will be prevented anyway if the user
  tries to reapprove the post.

app/models/post.rb

@@ -273,7 +273,7 @@ class Post < ApplicationRecord
 
   module ApprovalMethods
     def is_approvable?(user = CurrentUser.user)
-      !is_status_locked? && (is_pending? || is_flagged? || is_deleted?) && uploader != user && !approved_by?(user)
+      !is_status_locked? && (is_pending? || is_flagged? || is_deleted?) && uploader != user
     end
 
     def flag!(reason, is_deletion: false)
@@ -288,10 +288,6 @@ class Post < ApplicationRecord
       approvals.create(user: approver)
     end
 
-    def approved_by?(user)
-      approver == user || approvals.where(user: user).exists?
-    end
-
     def disapproved_by?(user)
       PostDisapproval.where(:user_id => user.id, :post_id => id).exists?
     end
@@ -989,7 +985,7 @@ class Post < ApplicationRecord
     end
 
     def has_active_pools?
-      !pools.undeleted.empty?
+      pools.undeleted.present?
     end
 
     def belongs_to_pool?(pool)

app/models/post_approval.rb

@@ -20,7 +20,7 @@ class PostApproval < ApplicationRecord
       errors.add(:base, "You cannot approve a post you uploaded")
     end
 
-    if post.approved_by?(user)
+    if post.approver == user || post.approvals.where(user: user).exists?
       errors.add(:base, "You have previously approved this post and cannot approve it again")
     end
   end