Fix x-mask triggering update requests on load

[joshhanley]

Currently if you have are using x-mask with Livewire and you are using wire:model.live, x-mask is triggering a network request on page load and changing the default value from null to an empty string.

Loading the below Volt component immediately triggers a request and the dd() is called.

This PR fixes it by adding a check to see if the _x_model value is the same as what is being set by the mask and skips the set. Or if the set value is an empty string and the _x_model value is null then it will also skip it. This is only for the initial load of the mask. Everything else should still run the same.

Fixes livewire/flux#751

<?php

use Livewire\Volt\Component;

new class extends Component {
    public $phone_number_masked;
    public $phone_number;

    public function updated()
    {
        dd('masked', $this->phone_number_masked, 'not masked', $this->phone_number);
    }
};

?>

<div>
    <input type="text" wire:model.live="phone_number_masked" x-mask="99999-999999" />
    <input type="text" wire:model.live="phone_number" />
</div>

[filiptaka]

This fix doesn't fully fix the issue (Tested in filament/livewire). In Filament the el._x_model.get() is undefined which is not the same as null.
So it should probably require another line:

                if (el._x_model.get() === undefined && el.value === '') return

[billmn]

Any update about this?