Bug when unpack specifc data

The following code throws an erro:
```php
bin = new Binn();
$data = $this->bin->serialize([
[
"Astrá",
6,
]
]);
$this->bin->unserialize($data);
```
Error:
```
ErrorException {#2094 ▼ // vendor\knik\binn\src\BinnAbstract.php:457
#message: "unpack(): Type C: not enough input values, need 1 values but only 0 were provided"
#code: 0
#file: "
C:\Users\Administrator\Desktop\workspace\PCare\vendor
\knik\binn\
src\BinnAbstract.php"
#line: 454
#severity: E_WARNING
```

The error disapear if:

- If I remove the number in the end of the array
- If I remove the string element
- If I swap the order of the elements in array
- If the array is only one deep
- If I remove the character 'á'

If I add other elements to array in any order, the exception occurr in the same way.