Avoid closing fromServerReader in case of null

src/main/java/ChatClient.java

@@ -69,11 +69,13 @@ public class ChatClient extends JFrame implements KeyListener {
                 }
             }
 
+            if (null != fromServerReader) {
                 try {
                     fromServerReader.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
+            }
 
             toServerWriter.close();