Fix form validation in user availability edit page.

Nah, it's not that big :P

Well then it's just a matter of taste :)
To me, it's easier to read the way it was before, because you have everything you need to understand the code in a couple of lines and you don't need to go back and forth to see what each variable is.  Moreover by using the `get` method in the case of `is_replaced`, you are masking the fact that it could be either `None` or `False` . Personally, I tend to favor the more explicit version.