We can set the physics flag in the room. And we can use physics_world_create() to create a physics system in a room... But it doesn't seem like we can check to see if a physics system currently exists. I'd like to roll out an all-in-one pause solution, but calling physics_pause_enable() agnostically in a room that doesn't have a physics system throws an error. How can I make a call to pause a physics system conditional on there actually being a physics system?