Optional peek distance values

[callumbwhyte]

When configuring distance values, such as with peek, all options must be supplied else Glide fails to render.

This works:

{
    peek: {
        before: 50,
        after: 100
    }
}

But setting only a single property breaks:

{
    peek: {
        before: 50
    }
}

This is because peek.after is NaN which then breaks the various calculations.

My changes ensure toInt and toFloat will always return a default value of 0, which ensures calculations continue to work.

[jedrzejchalubek]

This fallback needs to be done at the Peek component. The utility functions should not have this kind of logic.