PIE Seamless Travel with a standalone level instance causes assert in UWorldPartition::BeginDestroy

This check is hit on the server instance while it is performing garbage collection during the seamless travel. During this garbage collection, it will determine that the UWorldPartition object belonging to the client's Level Instance is unreachable, and it will attempt to destroy the UWorldPartition before the client instance is able to properly clean up the world and uninitialize the UWorldPartition object.

1. In a world partition level, add a Level Instance and set its "Level Behavior" to "Standalone" (this is necessary so this Level Instance will have its own associated UWorldPartition object).
2. In single-process PIE, connect a server and client.
3. Initiate a seamless travel on the server
4. Observe the check in UWorldPartition::BeginDestroy fails:
check(InitState == EWorldPartitionInitState::Uninitialized);