Fix crash in item_location serialization

[mqrause]

Summary

None

Purpose of change

Fixes #62078
Fixes #62954

Describe the solution

Check container location before accessing it.
Move activity backlog deserialization to after character id deserialization because item locations on character depend on the id being loaded. Kind of a followup to #54323.

Describe alternatives you've considered

Testing

1. Make character wearing backpack with filthy military rucksack inside the backpack, washing kit, enough soap (11) and water (88) to wash the rucksack
2. Spawn a distraction nearby
3. Start washing the rucksack and cancel it when the distraction query pops up
4. Remove the distraction
5. Start washing the rucksack again and finish it
6. Wear the rucksack and take off the backpack
7. Save the game

Saving would trigger the crash without this fix, now it doesn't.
The stale activity with stale item_locations will still be in the backlog and cause errors when loading, but they can be ignored.

Additional context