fix native crash by null material bug

Author: zxx43

cocos/particle/renderer/particle-system-renderer-cpu.ts

@@ -747,6 +747,12 @@ export default class ParticleSystemRendererCPU extends ParticleSystemRendererBas
         this._defines[ROTATION_OVER_TIME_MODULE_ENABLE] = enable;
         this._defines[INSTANCE_PARTICLE] = this._useInstance;
 
+        const matIns: MaterialInstance | null = ps.getMaterialInstance(0);
+        if (matIns === null || matIns === undefined) {
+            ps.setSharedMaterial(mat.parent, 0); // set material[0] as material for ui-mesh-renderer to use
+            ps.setMaterialInstance(mat, 0);
+        }
+
         mat.recompileShaders(this._defines);
         if (this._model) {
             this._model.updateMaterial(mat);