RFR: JDK-8147862 - Null check too late in sun.net.httpserver.ServerImpl

[Mark Sheppard]

Hi
    please oblige and review the small change
http://cr.openjdk.java.net/~msheppar/8147862/webrev/

to address
https://bugs.openjdk.java.net/browse/JDK-8147862

it was observed that  a null check on a SocketChannel object in
the Disptacher.run() method within ServerImpl, should be
earlier in the call flow.

regards
Mark