Fix css class assignment in issue custom field rendering in show view
Rendering the issue custom fields in the show view is done by the
class IssueFieldsRow, which can be found in issues_helper.rb.
The method IssueFieldRow#to_html has an error because the
class 'splitcontentright' will never be assigned.
This patch fixes this error by modifying the class in the respective
content_tag of the helper method. Thus, it is a one liner.