venus: fix empty submits with BOs

Empty submits with BOs (!batch_count && bo_count) were incorrectly
skipped.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11791>

src/virtio/vulkan/vn_renderer_virtgpu.c

@@ -542,6 +542,17 @@ sim_submit(struct virtgpu *gpu, const struct vn_renderer_submit *submit)
       }
    }
 
+   if (!submit->batch_count && submit->bo_count) {
+      struct drm_virtgpu_execbuffer args = {
+         .bo_handles = (uintptr_t)gem_handles,
+         .num_bo_handles = submit->bo_count,
+      };
+
+      ret = drmIoctl(gpu->fd, DRM_IOCTL_VIRTGPU_EXECBUFFER, &args);
+      if (ret)
+         vn_log(gpu->instance, "failed to execbuffer: %s", strerror(errno));
+   }
+
    free(gem_handles);
 
    return ret;