The solution I posted works for most use cases, but apparently Safari can have zombie windows with no tabs. I quit and restarted, and updated the script to hand

The solution I posted works for most use cases, but apparently Safari can have zombie windows with no tabs. I quit and restarted, and updated the script to handle the situation where there are no windows, but I need to wait until there are zombie tabs again to double-check that my fix for that works. Once that's done I'll post again.