[Peek] The Runner PID is not validated, resulting in a zombie process

### Microsoft PowerToys version

0.100.2

### Installation method

GitHub

### Area(s) with issue?

Peek

### Steps to reproduce

1. Open PowerShell
2. Enter:

```pwsh
\PowerToys.Peek.UI.exe 9999999
```

### ✔️ Expected Behavior

An error is reported and logged, as there is no Process ID with that number and no folder in the current path with that name.

### ❌ Actual Behavior

Peek opens but presents no UI, and must be ended via Task Manager:

### Upload Bug Report ZIP-file

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### Additional Information

_No response_

### Other Software

_No response_