Added emptynonzero model behavior

Check if it is good for you.

I tested for you
```php
		return (($value === $this->null_value) || empty($value))
			&& !($this->filterzero && $value === "0");
```
Result:
```
// Value 	 Zero 	 Result
// NULL 	 0 		 (1 || 1) && !(0 && 0) = (1 || 1) && 1 = 1
// "" 		 0 		 (1 || 1) && !(0 && 0) = (1 || 1) && 1 = 1
// 0 		 0 		 (1 || 1) && !(0 && 1) = (1 || 1) && 1 = 1
// NULL 	 1 		 (1 || 1) && !(1 && 0) = (1 || 1) && 1 = 1
// "" 		 1 		 (1 || 1) && !(1 && 0) = (1 || 1) && 1 = 1
// 0 		 1 		 (1 || 1) && !(1 && 1) = (1 || 1) && 0 = 0
```
Where `Zero` is the behavior enabled or not.