Re-throw http.ErrAbortHandler from our panic handler.

This aborts the response to the client and doesn't log an error.

httputil.ReverseProxy commonly panics with this error.

This results in different behavior from simply swallowing the panic.
Panicking prevents flushing the response to the client, and in the case
of a panic from httputil.ReverseProxy it results in clients potentially
receiving an empty response instead of what was already written to
http.ResponseWriter. This behavior is the same as if the panic handler
hadn't been installed.

src/main.go

@@ -127,6 +127,9 @@ func panicHandler(handler http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		defer func() {
 			if err := recover(); err != nil {
+				if err, ok := err.(error); ok && errors.Is(err, http.ErrAbortHandler) {
+					panic(http.ErrAbortHandler)
+				}
 				logc.Printf(r.Context(), "panic: %s %s %s: %s\n%s",
 					r.Method, r.Host, r.URL.Path, err, string(debug.Stack()))
 				http.Error(w,