Fix crash when calling setPose service on static and nolink entity (#2988)

Gazebo allows loading static models without any links. However, if a /world/<world>/set_pose service call is made targeting such a model, the physics system crashes , because the underlying physics code assumes every model has at least one link.
After Fix : Before executing set_pose, the code now checks whether the target model contains at least one link.


---------

Signed-off-by: momo <[email protected]>
Co-authored-by: Ian Chen <[email protected]>

Author: XINJIANGMO

src/systems/physics/Physics.cc

@@ -2485,6 +2485,14 @@ void PhysicsPrivate::UpdatePhysics(EntityComponentManager &_ecm)
                 << std::endl;
           return true;
         }
+        sim::Model model(_entity);
+        if (model.Links(_ecm).empty())
+        {
+            gzerr << "SetPose is not supported for models without any link."
+                  << "Entity [" << _entity << "]."
+                  << "Request ignored" << std::endl;
+            return true;
+        }
         auto modelPtrPhys = this->entityModelMap.Get(_entity);
         if (nullptr == modelPtrPhys)
           return true;