fix: finalize particle validation drawable

src/mbgl/renderer/layers/render_particle_validation_layer.cpp

@@ -120,6 +120,7 @@ void RenderParticleValidationLayer::update(gfx::ShaderRegistry&,
     drawable->setIsCustom(true);
     drawable->setRenderPass(RenderPass::Translucent);
     drawable->addTweaker(std::make_shared<ParticleValidationDrawableTweaker>(getID(), active, getLayerIndex()));
+    builder->flush(context);
     auto drawables = builder->clearDrawables();
     group->addDrawable(std::move(drawables.front()));
     ++stats.drawablesAdded;