HPCC-18193 Return fail on wait_read POLLHUP event

Signed-off-by: Mark Kelly <mark.kelly@lexisnexisrisk.com>

system/jlib/jsocket.cpp

@@ -1624,6 +1624,16 @@ int CSocket::wait_read(unsigned timeout)
                 errno = logPollError(fds[0].revents, "wait_read");
                 ret = -1;
             }
+            else if (fds[0].revents & POLLHUP)
+            {
+                // with poll() we can now differentiate this event from select()
+                // used to be that this fell thru ok and recv() would return 0
+                // indicating the socket has been closed, but the errno in that
+                // case could be misleading (ETIMEDOUT etc.)
+                LOGERR2(998,5,"wait_read POLLHUP");
+                errno = ENOTCONN;
+                ret = -1;
+            }
             else
             {
                 // POLLIN | POLLHUP ok