Fixes uploading of empty files (#25115).

- prevents creation of attachment records without existing diskfile and empty
  digest
- adds test case to check file upload API response
- also removes the file size check in ActsAsAttachable which still prevented
  attachment of zero size attachments to containers but only for clients
  without Javascript (where save_attachments is called with the actual file
  upload).
  
Patch by Jens Kraemer.

git-svn-id: http://svn.redmine.org/redmine/trunk@16341 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/integration/api_test/attachments_test.rb

@@ -197,4 +197,23 @@ class Redmine::ApiTest::AttachmentsTest < Redmine::ApiTest::Base
       end
     end
   end
+
+  test "POST /uploads.json should create an empty file and return a valid token" do
+    set_tmp_attachments_directory
+    assert_difference 'Attachment.count' do
+      post '/uploads.json', '', {"CONTENT_TYPE" => 'application/octet-stream'}.merge(credentials('jsmith'))
+      assert_response :created
+
+    end
+
+    json = ActiveSupport::JSON.decode(response.body)
+    assert_kind_of Hash, json['upload']
+    token = json['upload']['token']
+    assert token.present?
+
+    assert attachment = Attachment.find_by_token(token)
+    assert_equal 0, attachment.filesize
+    assert attachment.digest.present?
+    assert File.exist? attachment.diskfile
+  end
 end