fix: prevent exception when showing despawned NetworkObject - up port of #3029

[NoelStephensUnity]

Up-port of #3029

This resolves an issue where a NetworkObject component could be despawned or its GameObject destroyed in the same frame prior to attempting to show it.

MTTB-377

fix: #3023

Changelog

• Fixed: Issue where the NetworkSpawnManager.HandleNetworkObjectShow could throw an exception if one of the NetworkObject components to show was destroyed during the same frame.

Testing and Documentation

• Includes integration test NetworkVisibilityTests.HideShowAndDeleteTest.
• No documentation changes or additions were necessary.