CP fails to generate gateway cluster if no Timeout policy is defined for the destination

[wjrbetts]

What happened?

With no Timeout policy for a destination, the control plane crashes when trying to generate gateway cluster config:

[signal SIGSEGV: segmentation violation code=0x1 addr=0x10 pc=0x19e3337]

goroutine 1171 [running]:
github.com/kumahq/kuma/pkg/plugins/runtime/gateway.newClusterBuilder({0x232babc, 0x2}, {0x232d217, 0x4}, 0xc001979620)
        /home/circleci/project/pkg/plugins/runtime/gateway/cluster_generator.go:175 +0xd7
github.com/kumahq/kuma/pkg/plugins/runtime/gateway.(*ClusterGenerator).generateMeshCluster(0x7f37ae13a108?, 0xc0015a5a10, {0xc000228780, 0xc001700b88, 0xc001b0c2a0, 0xc0019795c0, {0x20fb, 0x5, {0xc000d43b20, 0x1e}, ...}, ...}, ...)
        /home/circleci/project/pkg/plugins/runtime/gateway/cluster_generator.go:126 +0xe5
github.com/kumahq/kuma/pkg/plugins/runtime/gateway.(*ClusterGenerator).GenerateClusters(0x1?, {0xc000e35740, {{0xc0018785a0, 0x2c}, 0xc0015a5a10, {0xc0015a79e0, 0xc0015a7a10}, 0xc001871770, 0xc001871860, 0xc001871890, ...}}, ...)
        /home/circleci/project/pkg/plugins/runtime/gateway/cluster_generator.go:72 +0x4f3
github.com/kumahq/kuma/pkg/plugins/runtime/gateway.Generator.generateRDS({{0xc00096f0e0}, {{_, _}}, {_, _}}, {0xc000e35740, {{0xc0018785a0, 0x2c}, 0xc0015a5a10, {0xc0015a79e0, ...}, ...}}, ...)
        /home/circleci/project/pkg/plugins/runtime/gateway/generator.go:272 +0x446
github.com/kumahq/kuma/pkg/plugins/runtime/gateway.Generator.Generate({{0xc00096f0e0}, {{0xc0000760d9, 0x8}}, {0xc0000760d9, 0x8}}, {0xc000e35740, {{0xc0018785a0, 0x2c}, 0xc0015a5a10, {0xc0015a79e0, ...}, ...}}, ...)
        /home/circleci/project/pkg/plugins/runtime/gateway/generator.go:224 +0x35e
github.com/kumahq/kuma/pkg/xds/generator/core.CompositeResourceGenerator.Generate({0xc0003d2af0, 0x7, 0xaa?}, {0xc000e35740, {{0xc0018785a0, 0x2c}, 0xc0015a5a10, {0xc0015a79e0, 0xc0015a7a10}, 0xc001871770, ...}}, ...)
        /home/circleci/project/pkg/xds/generator/core/resource_generator.go:19 +0x123
github.com/kumahq/kuma/pkg/xds/generator.(*ProxyTemplateProfileSource).Generate(0xc001b22ed0, {0xc000e35740, {{0xc0018785a0, 0x2c}, 0xc0015a5a10, {0xc0015a79e0, 0xc0015a7a10}, 0xc001871770, 0xc001871860, 0xc001871890, ...}}, ...)
        /home/circleci/project/pkg/xds/generator/proxy_template.go:73 +0x9d
github.com/kumahq/kuma/pkg/xds/generator.(*ProxyTemplateGenerator).Generate(0xc001b23188, {0xc000e35740, {{0xc0018785a0, 0x2c}, 0xc0015a5a10, {0xc0015a79e0, 0xc0015a7a10}, 0xc001871770, 0xc001871860, 0xc001871890, ...}}, ...)
        /home/circleci/project/pkg/xds/generator/proxy_template.go:25 +0x468
github.com/kumahq/kuma/pkg/xds/server/v3.(*templateSnapshotGenerator).GenerateSnapshot(_, {0xc000e35740, {{0xc0018785a0, 0x2c}, 0xc0015a5a10, {0xc0015a79e0, 0xc0015a7a10}, 0xc001871770, 0xc001871860, 0xc001871890, ...}}, ...)
        /home/circleci/project/pkg/xds/server/v3/reconcile.go:164 +0xc8
github.com/kumahq/kuma/pkg/xds/server/v3.(*reconciler).Reconcile(0xc000541b00, {0xc000e35740, {{0xc0018785a0, 0x2c}, 0xc0015a5a10, {0xc0015a79e0, 0xc0015a7a10}, 0xc001871770, 0xc001871860, 0xc001871890, ...}}, ...)
        /home/circleci/project/pkg/xds/server/v3/reconcile.go:57 +0x19d
github.com/kumahq/kuma/pkg/xds/sync.(*DataplaneWatchdog).syncDataplane(0xc00157eea0)
        /home/circleci/project/pkg/xds/sync/dataplane_watchdog.go:118 +0x4bb
github.com/kumahq/kuma/pkg/xds/sync.(*DataplaneWatchdog).Sync(0xc00157eea0)
        /home/circleci/project/pkg/xds/sync/dataplane_watchdog.go:60 +0x125
github.com/kumahq/kuma/pkg/xds/sync.(*dataplaneWatchdogFactory).New.func2()
        /home/circleci/project/pkg/xds/sync/dataplane_watchdog_factory.go:43 +0x9d
github.com/kumahq/kuma/pkg/util/watchdog.(*SimpleWatchdog).Start(0xc0016a43a0, 0xc0012994a0)
        /home/circleci/project/pkg/util/watchdog/watchdog.go:25 +0xe2
created by github.com/kumahq/kuma/pkg/xds/server/callbacks.(*dataplaneSyncTracker).OnProxyConnected
        /home/circleci/project/pkg/xds/server/callbacks/dataplane_sync_tracker.go:55 +0x40a```