Don't dereference NULL pointer on OOM

Fixes #37.

endlessh.c

@@ -790,7 +790,7 @@ main(int argc, char **argv)
                 if (!client) {
                     fprintf(stderr, "endlessh: warning: out of memory\n");
                     close(fd);
-                }
+                } else {
                     fifo_append(fifo, client);
                     logmsg(LOG_INFO, "ACCEPT host=%s port=%d fd=%d n=%d/%d",
                             client->ipaddr, client->port, client->fd,
@@ -798,6 +798,7 @@ main(int argc, char **argv)
                 }
             }
         }
+    }
 
     fifo_destroy(fifo);
     statistics_log_totals(0);