Fix error & head handling in stream handlers

This ensures that errors result in a client response failure, and that
headers are flushed without waiting for the stream to start.

This approach is a little basic, and errors don't yet handle this case
of browser streams, but I think those are very rarely used and it's
unlikely to be relevant.

Author: pimterry

src/rules/requests/request-handlers.ts

@@ -274,8 +274,12 @@ export class StreamHandler extends StreamHandlerDefinition {
             if (this.headers) dropDefaultHeaders(response);
 
             writeHead(response, this.status, undefined, this.headers);
+            response.flushHeaders();
+
             this.stream.pipe(response);
             this.stream.done = true;
+
+            this.stream.on('error', (e) => response.destroy(e));
         } else {
             throw new Error(stripIndent`
                 Stream request handler called more than once - this is not supported.