Fix bug when decoding multiple arrays

The decoder did not recognize trailing semi-colons when decoding arrays. Thus, a session like this:
```
array1|a:1:{s:5:\"test1\";b:1;};array2|a:1:{s:5:\"test2\";b:1;};
```
would result in a `PhpSessionData` map with the keys `array1` and `;array2`. This change will optionally read the trailing semi-colon after decoding an array, ensuring that the two keys are `array1` and `array2`.