Null pointer crash in receiveSyncChanges via DehydratedDevices

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Hello, I am not sure if this is the right place for creating this issue, or if it's an existing issue that's fixed.

## Description

`OlmMachine.receiveSyncChanges` crashes with `"null pointer passed to rust"` when processing device list sync data that involves DehydratedDevices. The crash occurs because the `DehydratedDevices` struct accesses a `Device` reference that is null.

This is unrecoverable — it kills the WASM OlmMachine and prevents all further crypto operations, including room key delivery for message decryption.

## Environment

- `matrix-js-sdk`: 40.1.0
- `@matrix-org/matrix-sdk-crypto-wasm`: ^17.0.0 (resolved via matrix-js-sdk dependency)
- Browser: Chrome 133 (macOS)
- Trigger: Normal `/sync` response processing with bridged rooms (mautrix bridges)

## Steps to Reproduce

1. Initialize MatrixClient with Rust crypto (`initRustCrypto`)
2. Start sync loop
3. Receive a `/sync` response that includes `device_lists` updates
4. `processDeviceLists` calls `receiveSyncChanges({ devices })`
5. The WASM `olmMachine.receiveSyncChanges()` crashes with: `Error: null pointer passed to rust`

## Stack Trace

```
Error: null pointer passed to rust
at OlmMachine.receiveSyncChanges (matrix_sdk_crypto_wasm_bg.wasm)
at RustCrypto.receiveSyncChanges (rust-crypto.js)
```

## Impact

- **Critical**: The crash kills the OlmMachine entirely — no further crypto operations are possible
- All message decryption stops after the crash
- Room key shares delivered via to-device messages are also lost if a catch-all handler returns `[]`

## Current Workaround

We wrap `receiveSyncChanges` to catch the null pointer error and retry without the `devices` parameter, so that to-device events (key shares) are still processed while the problematic device list processing is skipped:

```javascript
const original = crypto.receiveSyncChanges.bind(crypto);
crypto.receiveSyncChanges = async (args) => {
try {
return await original(args);
} catch (err) {
if (err.message?.includes("null pointer")) {
// Retry without device lists to preserve key share processing
const { devices, ...stripped } = args;
return await original(stripped);
}
throw err;
}
};
```

## Expected Behavior

`receiveSyncChanges` should handle null/missing Device references in DehydratedDevices gracefully instead of crashing.

## Additional Context

The crash appears related to the DehydratedDevices struct accessing a Device that was never initialized. This may be triggered by specific device list configurations from mautrix bridge bots.

Start at processDeviceLists and RustCrypto.receiveSyncChanges in rust-crypto.js, then inspect the OlmMachine.receiveSyncChanges entry point and the DehydratedDevices handling described in the report. Reproduce with a /sync response containing device-list updates from bridged rooms, and verify that missing Device references no longer crash the WASM OlmMachine while to-device key shares continue processing.

Written by the indexing model from the issue text.