VAAPI encoder crashes on AMD Polaris (RX 590)

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### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your issue described in the documentation?

- [x] I have read the documentation

### Is your issue present in the latest beta/pre-release?

This issue is present in the latest pre-release

### Describe the Bug

When using vaapi + kwin, starting streaming crashes immediately on AMD Polaris series graphics cards (RX 590 GME).
Configure vaapi encoder, kwin capture
Start Sunshine streaming
The entire software crashes.

### Expected Behavior

The VAAPI encoder should work normally.

### Additional Context

Changing n_dmabuf_infos > 0 at pipewire.cpp:883 to 0 forces the va_ram_t path (CPU copy path), and VAAPI encoding works normally again without crashing.
https://github.com/aningQwQ/Sunshine/tree/pr1

### Host Operating System

Linux

### Operating System Version

fedora44-kde-7.0.12-201.fc44.x86_64 (64 位)

### Architecture

amd64/x86_64

### Package

Linux - Fedora Copr

### GPU Type

AMD

### GPU Model

RX 590

### GPU Driver/Mesa Version

Mesa 26.0.8

### Capture Method

Kwin

### Apps

```json

```

### Log output

```shell
(Could not obtain due to webui crash, see online logs below)
```

### Online logs

https://gist.github.com/aningQwQ/9f7cdb5834603d4ff8561dae9954ec71

Start by reviewing the n_dmabuf_infos handling at pipewire.cpp:883 and the linked online logs for the KWin capture and VAAPI crash. Reproduce streaming with VAAPI on an AMD RX 590 under Linux, then confirm that KWin capture starts without crashing while retaining the normal DMA-BUF path.

Written by the indexing model from the issue text.