Fix #5150: rating: metatag doesn't work on betabooru upload page.

app/models/post.rb

@@ -15,6 +15,7 @@ class Post < ApplicationRecord
   normalize :source, :normalize_source
   before_validation :merge_old_changes
   before_validation :normalize_tags
+  before_validation :apply_pre_metatags
   before_validation :blank_out_nonexistent_parents
   before_validation :remove_parent_loops
   validates :md5, uniqueness: { message: ->(post, _data) { "Duplicate of post ##{Post.find_by_md5(post.md5).id}" }}, on: :create
@@ -23,7 +24,6 @@ class Post < ApplicationRecord
   validates :source, length: { maximum: 1200 }
   validate :post_is_not_its_own_parent
   validate :uploader_is_not_limited, on: :create
-  before_save :apply_pre_metatags
   before_save :parse_pixiv_id
   before_save :added_tags_are_valid
   before_save :removed_tags_are_valid

test/unit/post_test.rb

@@ -745,6 +745,14 @@ class PostTest < ActiveSupport::TestCase
               assert_equal("q", @post.rating)
             end
           end
+
+          context "when a post is created" do
+            should "set the rating" do
+              @post = create(:post, tag_string: "tagme rating:e", rating: nil)
+
+              assert_equal("e", @post.rating)
+            end
+          end
         end
 
         context "for a fav" do