Flaky test check_runtimes: [03:55:11]RUNTIME: Cannot read null.assigned_equipment_preset - code/game/objects/items/devices/radio/headset.dm@379

Flaky tests were detected in [this test run](https://github.com/cmss13-devs/cmss13/actions/runs/28145621179/attempts/1). This means that there was a failure that was cleared when the tests were simply restarted.
Failures:
```
check_runtimes: [03:55:11]RUNTIME: Cannot read null.assigned_equipment_preset - code/game/objects/items/devices/radio/headset.dm@379 at code/defines/../modules/unit_tests/check_runtimes.dm:10
```

Start with code/game/objects/items/devices/radio/headset.dm around line 379 and the check_runtimes test at code/modules/unit_tests/check_runtimes.dm:10. Reproduce the reported test run and trace the null assigned_equipment_preset access; done means repeated test runs no longer report this runtime.

Written by the indexing model from the issue text.