Answer 500 to an exception the exception handler gives no status

An exception handler that set no status sent its response with 200, or
with whatever status the throwing handler had set. The status is now
set to 500 before the exception handler runs, as ASP.NET Core does, so
it stays 500 unless the exception handler sets another one.

On a WebSocket upgrade, an exception from the pre-routing handler, the
pre-request handler or the sub-protocol selector skipped the exception
handler and dropped the connection without a response. Everything
before the protocol switches now goes through the same exception
handling as routing, so it is answered over HTTP. The WebSocket handler
itself still runs outside it.

README.md

@@ -522,7 +522,7 @@ svr.set_error_handler([](const auto& req, auto& res) {
 ```
 
 ### Exception handler
-The exception handler gets called if a user routing handler throws an error. This covers the pre-routing handler, the file request handler, the pre-request handler, route handlers and content readers. An exception from the post-routing handler, the error handler, the `Expect: 100-continue` handler, a content provider, a logger or a WebSocket handler does not reach it: the connection is dropped, and the error logger receives `Error::UserCallbackException`.
+The exception handler gets called if a user routing handler throws an error. This covers the pre-routing handler, the file request handler, the pre-request handler, route handlers, content readers and, on a WebSocket upgrade, the sub-protocol selector. The response is a 500 unless the exception handler sets another status. An exception from the post-routing handler, the error handler, the `Expect: 100-continue` handler, a content provider, a logger or a WebSocket handler does not reach it: the connection is dropped, and the error logger receives `Error::UserCallbackException`.
 
 ```cpp
 svr.set_exception_handler([](const auto& req, auto& res, std::exception_ptr ep) {