deleting prior assistant chat crashes Android app

### ⚠️ Before posting ⚠️

- [x] This is a **bug**, not a question or an enhancement.
- [x] I've [searched for similar issues](https://github.com/nextcloud/android/issues) and didn't find a duplicate.
- [x] I've written a clear and descriptive title for this issue, not just "Bug" or "Crash".
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/).

### Steps to reproduce

In assistant screen in Android app, go to history, long press prior chat to select it ->delete. App tries to bring up biometric verification and crashes.

### Expected behaviour

Should just delete the prior chat

### Actual behaviour

Crashes

### Android version

16

### Device brand and model

Pixel 9a

### Stock or custom OS?

Stock

### Nextcloud android app version

33.1.0

### Nextcloud server version

33.0.3

### Using a reverse proxy?

Yes

### Android logs

### Cause of error
```java
Exception in thread "DefaultDispatcher-worker-5" java.lang.NumberFormatException: For input string: "null"
at java.lang.Long.parseLong(Long.java:740)
at java.lang.Long.parseLong(Long.java:863)
at com.nextcloud.client.assistant.conversation.ConversationViewModel$deleteConversation$1.invokeSuspend(ConversationViewModel.kt:97)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:101)
at kotlinx.coroutines.internal.LimitedDispatcher$Worker.run(LimitedDispatcher.kt:113)
at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:89)
at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:589)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:823)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:720)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:707)

```

### App information
* ID: `com.nextcloud.client`
* Version: `330010090`
* Build flavor: `gplay`

### Device information
* Brand: `google`
* Device: `tegu`
* Model: `Pixel 9a`
* Product: `tegu`

### Firmware
* SDK: `36`
* Release: `16`
* Incremental: `15001963`

### Server error logs

```bash

```

### Additional information

_No response_