Add NaN logic to ASI flow

[Hoppyhob]

Closes #2441

• Added NaN Check to _onClickButton to reset assignments value to 0 if it is NaN or undefined.
• Added NaN check to getData() to return the assignment to 0 if NaN.
• Added check to set ability as fixed if ability's initial value matched the ability's max value.

[Fyorl]

Thanks for doing this work. In addition to the comment I left, I feel it would be preferable to prevent the value from ever becoming NaN at all rather than spreading NaN checks around our code. I believe the NaN value is originating in _onChangeInput where we call input.valueAsNumber. We should instead do something like this:

const value = isNaN(input.valueAsNumber) ? 0 : input.valueAsNumber;
const clampedValue = Math.clamped(value, Number(input.min), Number(input.max));

[Hoppyhob]

Added the requested changes and removed the NaN checks that are now redundant.
For the _onChangeInput I added a NaN check that directly sets the assignments[key] to zero. (Instead of setting value to zero then clamping it to the minimum then finding the difference) Otherwise if not NaN it will go through the original logic.

[Fyorl]

Nice, thanks, looks good to me