Console error handling fails when filesystem resource is not present.

[pstutz]

The headers would be sent twice, instead crashes with:
File server is handling:
java.io.IOException: headers already sent
at sun.net.httpserver.ExchangeImpl.sendResponseHeaders(ExchangeImpl.java:204)
at sun.net.httpserver.HttpExchangeImpl.sendResponseHeaders(HttpExchangeImpl.java:86)
at com.signalcollect.console.FileServer.handle(ConsoleServer.scala:356)
at com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:77)
at sun.net.httpserver.AuthFilter.doFilter(AuthFilter.java:83)
at com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:80)
at sun.net.httpserver.ServerImpl$Exchange$LinkHandler.handle(ServerImpl.java:668)
at com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:77)
at sun.net.httpserver.ServerImpl$Exchange.run(ServerImpl.java:640)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)