[BUG] Unhandled `null` in updateCombat hook, Turn Marker not removed from previous combatant when switching to a tokenless combatant.

[BoltsJ]

Describe the bug
In the hook for updateCombat starting at line 62 in turnmarker.js, an exception is thrown if a combatant has no token associated with it.

Environment Details
Foundry VTT Version: 0.7.5
Turn Marker Version: 2.6.9

To Reproduce
Steps to reproduce the behavior:

1. Set up a combat
2. run game.combat.addCombatant({ name: "DUMMY" });
3. Move the turn to the dummy combatant.
4. An uncaught exception is logged and the turn marker is not removed from the previous combatant until the next switch.

Expected behavior
The turn marker should be removed from the previous token, even if the next combatant has no token.

Screenshots

Additional context
I ran into this while developing a module that modifies the initiative behavior, but this occurs with no modules as well.