Spawners can "hijack" entities because of the `eid` property

[kuroppoi]

The owned entity ID of a spawner is currently stored in metablock property eid (which is stored on disk) and might point to a different entity when the server restarts.

Should either:

• Randomize entity IDs (they are currently incremental) which reduces the chance of this happening to practically zero (but not truly)
• Store the entity ID somewhere else or delete it on shutdown/startup (which requires specialized logic which is annoying)

[kuroppoi]

Good enough for now.