Prevent a double-close on the server side in some cases.

Alternate solution to a problem pointed out by @g-coder in pull request #429.

src/iperf_server_api.c

@@ -1,5 +1,5 @@
 /*
- * iperf, Copyright (c) 2014, 2015, The Regents of the University of
+ * iperf, Copyright (c) 2014, 2015, 2016, The Regents of the University of
  * California, through Lawrence Berkeley National Laboratory (subject
  * to receipt of any required approvals from the U.S. Dept. of
  * Energy).  All rights reserved.
@@ -410,8 +410,12 @@ static void
 cleanup_server(struct iperf_test *test)
 {
     /* Close open test sockets */
-    close(test->ctrl_sck);
-    close(test->listener);
+    if (test->ctrl_sck) {
+	close(test->ctrl_sck);
+    }
+    if (test->listener) {
+	close(test->listener);
+    }
 
     /* Cancel any remaining timers. */
     if (test->stats_timer != NULL) {
@@ -545,6 +549,7 @@ iperf_run_server(struct iperf_test *test)
                         if (test->no_delay || test->settings->mss || test->settings->socket_bufsize) {
                             FD_CLR(test->listener, &test->read_set);
                             close(test->listener);
+			    test->listener = 0;
                             if ((s = netannounce(test->settings->domain, Ptcp, test->bind_address, test->server_port)) < 0) {
 				cleanup_server(test);
                                 i_errno = IELISTEN;