FEATURE: do not switch to JPEG unless you meet 75k byte savings

This also adjusts the algorithm to expect

- 30% saving for JPEG conversion

AND

- Minimum of 75K bytes saved

The reasoning for increase of saving requirements is cause PNG may have been
uploaded unoptimized, 30% saving on PNG is very possible

spec/lib/upload_creator_spec.rb

@@ -99,13 +99,37 @@ RSpec.describe UploadCreator do
     end
 
     describe 'converting to jpeg' do
-      let(:filename) { "logo.png" }
+      let(:filename) { "should_be_jpeg.png" }
       let(:file) { file_from_fixtures(filename) }
 
+      let(:small_filename) { "logo.png" }
+      let(:small_file) { file_from_fixtures(small_filename) }
+
       before do
         SiteSetting.png_to_jpg_quality = 1
       end
 
+      it 'should not store file as jpeg if it does not meet absolute byte saving requirements' do
+
+        # logo.png is 2297 bytes, converting to jpeg saves 30% but does not meet
+        # the absolute savings required of 25_000 bytes, if you save less than that
+        # skip this
+
+        expect do
+          UploadCreator.new(small_file, small_filename,
+            pasted: true,
+            force_optimize: true
+          ).create_for(user.id)
+        end.to change { Upload.count }.by(1)
+
+        upload = Upload.last
+
+        expect(upload.extension).to eq('png')
+        expect(File.extname(upload.url)).to eq('.png')
+        expect(upload.original_filename).to eq('logo.png')
+
+      end
+
       it 'should store the upload with the right extension' do
         expect do
           UploadCreator.new(file, filename,
@@ -118,7 +142,7 @@ RSpec.describe UploadCreator do
 
         expect(upload.extension).to eq('jpeg')
         expect(File.extname(upload.url)).to eq('.jpeg')
-        expect(upload.original_filename).to eq('logo.jpg')
+        expect(upload.original_filename).to eq('should_be_jpeg.jpg')
       end
     end
   end