Fix panic in entity event processing

[plorenz]

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x2530333]

goroutine 6 [running]:
github.com/openziti/ziti/controller/events.(*entityChangeEventFilter).AcceptEntityChangeEvent(0x90?, 0xc0030b5c00?)
        /home/plorenz/work/nf/ziti/controller/events/dispatcher_entity_change.go:357 +0x33
github.com/openziti/ziti/controller/events.(*Dispatcher).AcceptEntityChangeEvent(0xc003417278?, 0xc004372000?)
        /home/plorenz/work/nf/ziti/controller/events/dispatcher_entity_change.go:60 +0x95
github.com/openziti/ziti/controller/events.(*entityChangeEventDispatcher).ProcessPostCommit(0xc000a37f00, {0x40bdbc0, 0xc003f40000})
        /home/plorenz/work/nf/ziti/controller/events/dispatcher_entity_change.go:288 +0x1a5
github.com/openziti/storage/boltz.(*untypedEntityConstraintWrapper[...]).ProcessPostCommit(...)
        /home/plorenz/go/pkg/mod/github.com/openziti/storage@v0.2.28/boltz/store_crud.go:729
github.com/openziti/storage/boltz.(*EntityChangeState[...]).processPostCommit(0xc005755f40)
        /home/plorenz/go/pkg/mod/github.com/openziti/storage@v0.2.28/boltz/store.go:185 +0xab
go.etcd.io/bbolt.(*Tx).Commit(0xc003417260)
        /home/plorenz/go/pkg/mod/go.etcd.io/bbolt@v1.3.8/tx.go:229 +0x3f2
go.etcd.io/bbolt.(*DB).Update(0xc005b78de0?, 0xc005b78de0)
        /home/plorenz/go/pkg/mod/go.etcd.io/bbolt@v1.3.8/db.go:893 +0xd2
github.com/openziti/storage/boltz.(*DbImpl).Update(0xc00042c960, {0x40bb408?, 0xc005755f40?}, 0xc005bfe940)
        /home/plorenz/go/pkg/mod/github.com/openziti/storage@v0.2.28/boltz/db.go:120 +0x19b
github.com/openziti/ziti/controller/model.(*ApiSessionManager).Create(0xc000e2af40, {0x40bb408, 0xc005755f40}, 0xc0034170a0, {0x0, 0x0, 0x0})
        /home/plorenz/work/nf/ziti/controller/model/api_session_manager.go:57 +0x125
github.com/openziti/ziti/controller/internal/routes.(*AuthRouter).authHandler.func1()
        /home/plorenz/work/nf/ziti/controller/internal/routes/authenticate_router.go:185 +0x85
github.com/openziti/ziti/controller/command.(*adaptiveRateLimiter).run(0xc000e2aec0)
        /home/plorenz/work/nf/ziti/controller/command/rate_limiter.go:340 +0x1b1
created by github.com/openziti/ziti/controller/command.NewAdaptiveRateLimiter in goroutine 1
        /home/plorenz/work/nf/ziti/controller/command/rate_limiter.go:230 +0x26f