Ensure PromiseRejectionEvent has reason before logging it (#1150)

Fixes #1149

## What is this PR doing?

Checks if `event.reason` or `event.reason.stack` exist in
`logUnhandledRejection`.

## What problem is it solving?

Fixes a JS error when a promise without a reason is thrown.

## How is the problem addressed?

By checking if a reason is provided.

## Testing Instructions

- Checkout this branch
- Start Playground `npm run dev`
- Open Playground and execute this in the browser console
```
Promise.reject();
```
- Confirm that logger doesn't throw an error

packages/php-wasm/logger/src/lib/logger.ts

@@ -76,7 +76,12 @@ export class Logger extends EventTarget {
 	 * @param PromiseRejectionEvent event
 	 */
 	private logUnhandledRejection(event: PromiseRejectionEvent) {
-		this.log(`${event.reason.stack}`, 'Error');
+		// No reason was provided, so we can't log anything.
+		if (!event?.reason) {
+			return;
+		}
+		const message = event?.reason.stack ?? event.reason;
+		this.log(message, 'Error');
 	}
 
 	/**