[giow] (3) Match reality: the label in <option label=''> is ignored if empty.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=27207
Affected topics: HTML

git-svn-id: https://svn.whatwg.org/webapps@8868 340c8d12-0b0e-0410-8428-c7bf67bfef74