Retain initial disabled/enabled state for bound options.

When I have an `enabled` binding handler on a select with an `options` binding handler, re-set of the options causes my state to change to enabled regardless of what it was before. This forces that state to stay.

I tried to write the test for it, but I wasn't sure how to run the test (I tried mocha but it throw an error) so I'm not entirely sure the test is correct. The code fix works for my project though.