Fix reconnect crash (EOCD) and building-placement NullReferenceException

[chrizZzt]

Fixes two independent crashes observed on Timberborn 1.0.13.1 / BeaverBuddies 1.7.1.

Fixes #193
Fixes #194

1. Reconnect crash — "End of Central Directory record could not be found" (#193)

After the host connection drops (SocketException: Connection refused), the client receives a short non-map payload (e.g. 213 bytes; real maps are ~420–460 KB) as its "first message". ClientConnectionService.LoadMap writes those bytes into a save and loads them, so ZipArchive throws during scene load (outside LoadMap, so a local try/catch can't catch it) and the game crashes.

Fix: validate the received bytes before loading — a Timberborn save is a ZIP, so it must start with the local-file-header magic PK\x03\x04 and have a minimum length. If the data isn't a valid save, show the existing connection-failed dialog (ShowError(null)) instead of loading a bogus save.

2. NullReferenceException in ReplayEvent.GetEntityID (#194)

When placing/duplicating a building, GetEntityID(DuplicationSource) calls component.GetComponent<EntityComponent>(), which throws internally in ComponentCache.GetIndex<T>() when the component isn't registered as an entity yet. The existing ?. only guards a null component, not an exception thrown inside GetComponent.

Fix: catch the exception and return null; callers already treat a null entity ID as "not an entity" and fall back to the base behaviour.

Notes

• Both changes are minimal and defensive; no protocol changes, so a patched client stays compatible with an unpatched host (and vice-versa).
• Verified the project builds against Timberborn 1.0.13.1 (Release Steam). I was not able to run an extensive multi-machine co-op session, so a second pair of eyes on the reconnect path is welcome.
• Diagnosed from five Error reports/*.zip crash dumps; details and logs are in the linked issues.

Co-authored with assistance from Claude Code.

[thomaswp]

Thanks for the issues and the PR. I'm traveling and won't be able to look at it until next week, but I'll get back to you then.