Fix 500 error page failover

[NuroDev]

Similar to the issue mentioned in #1, currently if you include a 500.astro page in your project this adapter does not return that page if the SSR page fails to render.

I imagine some tweaks need to just be made to this line to wrap it in a try/catch to make it return the 500.html page if app.render() fails.

[lilnasy]

It seems to be working just fine