Allow disabling x-mask with a falsy value

[stepanjakl]

Hi,

I have a specific use case for the Mask plugin, where the user selects an international phone code and the input value gets formatted accordingly.

However, the user should also have an option to type the number without being forced the format (in a case, the format is not available in the list). Example:

In the end, the example code looks like this:

x-mask:dynamic="selectValue ? `${options[selectValue].international} ${options[selectValue].format}` : false"

// Above translates to:
x-mask:dynamic="'cz' ? `+420 999 999 999` : false" --> +420 987 654 321

// Or:
x-mask:dynamic="null ? `` : false" --> no forced formatting

And that's what this PR allows for. Let me know if anything needs changing.

[calebporzio]

This makes a lot of sense - would you mind adding a test for it?

[stepanjakl]

@calebporzio Tests added

[calebporzio]

This is great, thanks!