fix PhysX Physics costs some time even there is not physics node in s…

…cene cocos#11382 (cocos#11396)

Co-authored-by: zhanling <[email protected]>

cocos/physics/physx/physx-world.ts

@@ -69,6 +69,7 @@ export class PhysXWorld extends PhysXInstance implements IPhysicsWorld {
     }
 
     step (deltaTime: number, _timeSinceLastCalled?: number, _maxSubStep = 0): void {
+        if (this.wrappedBodies.length === 0) return;
         this._simulate(deltaTime);
         if (!PX.MULTI_THREAD) {
             this._fetchResults();