Prevent onPropertyChanged being triggered if both values are NaN

This is something we fixed in CT and are now feeding it back to BRJS.

THe bug was that if you had a property with a value of `NaN` and you
called `setValue` with `NaN` again it would still trigger
`onPropertyChanged` even though the value hasn't really changed.
Merge pull request #688 from janhancic/develop-presenter-property-fix

Prevent onPropertyChanged being triggered if both values are NaN