FIX: should_alter_quality should respect png_to_jpg_quality (#12055)

`convert_to_jpeg!` is only called if `convert_png_to_jpeg?` and/or `should_alter_quality?` is true.

`convert_png_to_jpeg?` can be disabled by setting `SiteSetting.png_to_jpg_quality` to 100.

However, `should_alter_quality?` could be true if `SiteSetting.recompress_original_jpg_quality` was lower than the quality of the uploaded file, regardless of file type.

This commits changes `should_alter_quality?` so that uploaded png files will use the `SiteSetting.png_to_jpg_quality` value, rather than ``SiteSetting.recompress_original_jpg_quality` value.

lib/upload_creator.rb

@@ -276,7 +276,8 @@ class UploadCreator
   def should_alter_quality?
     return false if animated?
 
-    @upload.target_image_quality(@file.path, SiteSetting.recompress_original_jpg_quality).present?
+    desired_quality = @image_info.type == :png ? SiteSetting.png_to_jpg_quality : SiteSetting.recompress_original_jpg_quality
+    @upload.target_image_quality(@file.path, desired_quality).present?
   end
 
   def should_downsize?

spec/lib/upload_creator_spec.rb

@@ -134,6 +134,9 @@ RSpec.describe UploadCreator do
       let(:small_filename) { "logo.png" }
       let(:small_file) { file_from_fixtures(small_filename) }
 
+      let(:large_filename) { "large_and_unoptimized.png" }
+      let(:large_file) { file_from_fixtures(large_filename) }
+
       let(:animated_filename) { "animated.gif" }
       let(:animated_file) { file_from_fixtures(animated_filename) }
 
@@ -212,6 +215,23 @@ RSpec.describe UploadCreator do
           expect(upload.original_filename).to eq('animated.gif')
         end
 
+        context "png image quality settings" do
+          before do
+            SiteSetting.png_to_jpg_quality = 100
+            SiteSetting.recompress_original_jpg_quality = 90
+            SiteSetting.image_preview_jpg_quality = 10
+          end
+
+          it "should not convert to jpeg when png_to_jpg_quality is 100" do
+            upload = UploadCreator.new(large_file, large_filename, force_optimize: true).create_for(user.id)
+
+            expect(upload.extension).to eq('png')
+            expect(File.extname(upload.url)).to eq('.png')
+            expect(upload.original_filename).to eq('large_and_unoptimized.png')
+          end
+
+        end
+
         it 'should not convert animated WEBP images' do
           expect do
             UploadCreator.new(animated_webp_file, animated_webp_filename,