[Bugfix] Support substitution events with no replacement player

[DriesDeprest]

Currently, in our StatsPerform deserializer we potentially set the replacement_player as None in case the player off event is not directly followed by a player on event, which happens in approx 1% of the matches, see: https://github.com/PySport/kloppy/blob/master/kloppy/infra/serializers/event/statsperform/deserializer.py#L396-L406.

In order to support substitution events where no new sub on player is coming on the pitch for the sub off player, we add a check to see whether the replacement player actually exists prior to updating its position.

For context, a related discussion on substitution events: #362.

[probberechts]

If there is no other player coming on the pitch, it should not be counted as a subsitution, right? In Stats Perform data, these should be "Player retired" events.

Do you know why the replacement_player is missing? I have two hypotheses:

1. There is a player off event, but not necessarily as the next event? This should be addressed in the deserializer.
2. The event data is incomplete