FIX: Be able to handle long file extensions (#12375)

* FIX: Be able to handle long file extensions

Some applications have really long file extensions, but if we truncate
them weird behavior ensues.

This commit changes the file extension size from 10 characters to 255
characters instead.

See:

https://meta.discourse.org/t/182824

* Keep truncation at 10, but allow uppercase and dashes

spec/lib/upload_creator_spec.rb

@@ -9,7 +9,7 @@ RSpec.describe UploadCreator do
   describe '#create_for' do
     describe 'when upload is not an image' do
       before do
-        SiteSetting.authorized_extensions = 'txt'
+        SiteSetting.authorized_extensions = 'txt|long-FileExtension'
       end
 
       let(:filename) { "utf-8.txt" }
@@ -38,6 +38,19 @@ RSpec.describe UploadCreator do
         expect(user2.user_uploads.count).to eq(1)
         expect(upload.user_uploads.count).to eq(2)
       end
+
+      let(:longextension) { "fake.long-FileExtension" }
+      let(:file2) { file_from_fixtures(longextension) }
+
+      it 'should truncate long extension names' do
+        expect do
+          UploadCreator.new(file2, "fake.long-FileExtension").create_for(user.id)
+        end.to change { Upload.count }.by(1)
+
+        upload = Upload.last
+
+        expect(upload.extension).to eq('long-FileE')
+      end
     end
 
     describe 'when image is not authorized' do