Fix: missing null check leads to crash when rendering

The simulation cache is allocated lazily during evaluation when the
depsgraph is active. However, during rendering, the depsgraph is not
active, so it's not created.

source/blender/modifiers/intern/MOD_nodes.cc

@@ -1200,6 +1200,10 @@ static void prepare_simulation_states_for_evaluation(const NodesModifierData &nm
     }
   }
 
+  if (nmd_orig.simulation_cache == nullptr) {
+    return;
+  }
+
   /* Load read-only states to give nodes access to cached data. */
   const bke::sim::StatesAroundFrame sim_states =
       nmd_orig.simulation_cache->get_states_around_frame(current_frame);