Add exception handling to the server loop

This should start to deal with accept failing if there are too many
open files.

knots/web-server.scm

@@ -575,6 +575,14 @@ before sending back to the client."
   (sigaction SIGPIPE SIG_IGN)
 
   (spawn-fiber
+   (lambda ()
+     (while #t
+       (with-exception-handler
+           (const #t)
+         (lambda ()
+           (with-exception-handler
+               (lambda (exn)
+                 (print-backtrace-and-exception/knots exn))
              (lambda ()
                (let loop ()
                  (match (accept socket (logior SOCK_NONBLOCK SOCK_CLOEXEC))
@@ -588,7 +596,8 @@ before sending back to the client."
                                                 (post-request-hook/safe
                                                  post-request-hook)))
                                  #:parallel? #t)
-          (loop))))))
+                    (loop)))))))
+         #:unwind? #t))))
 
   (make-web-server socket
                    (vector-ref (getsockname socket)