The icinga2 connector stop with segmentation violation signal
## Description
The connector crash seems to occur when it gets a lot of alarms in Icinga.
```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x559d1bf09747]
goroutine 52 [running]:
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga.(*DisplayNameResolver).ResolveServiceName(0x1?, {0xc0000dda20, 0x6}, {0xc0000dda40?, 0x6?})
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga/display_name_resolver.go:33 +0x27
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga.(*DisplayNameResolver).ResolveNames(0xc0000ddb98?, {0xc0000dda20?, 0x6?}, {0xc0000dda40, 0x7})
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga/display_name_resolver.go:41 +0x27
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga.(*Listener).processEventStream(0xc00014e000, {0x559d1c1d9f00, 0xc0002a0140}, {0xc000422900?, 0x0?}, 0xc000206401?)
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga/listener.go:177 +0x346
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga.(*Listener).doLongPolling(0xc00014e000, {0x559d1c1d9f00, 0xc0002a0140})
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga/listener.go:152 +0x605
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga.(*Listener).Listen.func2()
git.canopsis.net/canopsis-connectors/connector-icinga2/lib/icinga/listener.go:99 +0x65
golang.org/x/sync/errgroup.(*Group).Go.func1()
golang.org/x/sync@v0.6.0/errgroup/errgroup.go:78 +0x56
created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 25
golang.org/x/sync@v0.6.0/errgroup/errgroup.go:75 +0x96
```
## Context
* Docker
* Icinga2 **2.15.0** / Icinga Web 2 **2.12.5**
* connector-icinga2 **24.04.2**
* Canopsis Pro **25.04.1**
## How to reproduce
1. Start Canopsis Pro with your docker compose.
2. Get the **new** [Icinga2 mock](https://git.canopsis.net/canopsis/mocks/monitoring/icinga2/-/tree/init-repo?ref_type=heads) and start it with `docker compose up -d` as indicated in the [README](https://git.canopsis.net/canopsis/mocks/monitoring/icinga2/-/blob/init-repo/README.md?ref_type=heads).
3. Look the container log: `docker logs -f canopsis-icinga-connector-1`
issue