Fix crash in Jolt Physics when switching scenes in editor

Co-authored-by: Jorrit Rouwe <jrouwe@gmail.com>

modules/jolt_physics/spaces/jolt_space_3d.cpp

@@ -436,6 +436,12 @@ void JoltSpace3D::remove_object(const JPH::BodyID &p_jolt_id) {
 	}
 
 	body_iface.DestroyBody(p_jolt_id);
+
+	// If we're never going to step this space, like in the editor viewport, we need to manually clean up Jolt's broad phase instead, otherwise performance can degrade when doing things like switching scenes.
+	// We'll never actually have zero bodies in any space though, since we always have the default area, so we check if there's one or fewer left instead.
+	if (!JoltPhysicsServer3D::get_singleton()->is_active() && physics_system->GetNumBodies() <= 1) {
+		physics_system->OptimizeBroadPhase();
+	}
 }
 
 void JoltSpace3D::flush_pending_objects() {

thirdparty/jolt_physics/Jolt/Physics/Collision/BroadPhase/BroadPhaseQuadTree.cpp

@@ -73,6 +73,7 @@ void BroadPhaseQuadTree::Optimize()
 {
 	JPH_PROFILE_FUNCTION();
 
+	// Free the previous tree so we can create a new optimized tree
 	FrameSync();
 
 	LockModifications();
@@ -80,7 +81,7 @@ void BroadPhaseQuadTree::Optimize()
 	for (uint l = 0; l < mNumLayers; ++l)
 	{
 		QuadTree &tree = mLayers[l];
-		if (tree.HasBodies())
+		if (tree.HasBodies() || tree.IsDirty())
 		{
 			QuadTree::UpdateState update_state;
 			tree.UpdatePrepare(mBodyManager->GetBodies(), mTracking, update_state, true);
@@ -90,6 +91,9 @@ void BroadPhaseQuadTree::Optimize()
 
 	UnlockModifications();
 
+	// Free the tree from before we created a new optimized tree
+	FrameSync();
+
 	mNextLayerToUpdate = 0;
 }
 

thirdparty/jolt_physics/Jolt/Physics/Collision/BroadPhase/QuadTree.cpp

@@ -301,7 +301,7 @@ void QuadTree::UpdatePrepare(const BodyVector &inBodies, TrackingVector &ioTrack
 #endif
 
 	// Create space for all body ID's
-	NodeID *node_ids = new NodeID [mNumBodies];
+	NodeID *node_ids = mNumBodies > 0? new NodeID [mNumBodies] : nullptr;
 	NodeID *cur_node_id = node_ids;
 
 	// Collect all bodies