handle some null/freed item cases to avoid bugs

[Invertex]

May fix #2381 but don't know for sure yet.

Regardless, this gets rid of some potential error spam that isn't useful to the end-user.

Sometimes the opener_events_stack items can be in the process of being freed, or have become Null by the time the code got there and causes an error trying to feed them into the create_and_branch_event() function.
Same with the _batches content.

[Jowan-Spooner]

Looks good generally, some testing would be nice.

[zaknafean]

Overall this does no harm and likely does fix some issues some people see, though I can't recreate the issues this was supposed to address consistently. My concern is this may be more a bandage to a core problem. But it isn't enough of a problem in my eyes to not merge up.