evas cserve2 - check fcntl return for setting non-block

fix CID 1039707

src/bin/evas/evas_cserve2_usage.c

@@ -79,7 +79,7 @@ _server_connect(void)
         return EINA_FALSE;
      }
 
-   fcntl(s, F_SETFL, O_NONBLOCK);
+   if (fcntl(s, F_SETFL, O_NONBLOCK) < 0) ERR("can't set non-blocking fd");
 
    socketfd = s;