Make fields volatile for thread safety

Author: maxcai314

core/src/main/java/org/nanohttpd/protocols/http/ServerRunnable.java

@@ -44,13 +44,13 @@
  */
 public class ServerRunnable implements Runnable {
 
-    private NanoHTTPD httpd;
+    private final NanoHTTPD httpd;
 
     private final int timeout;
 
-    private IOException bindException;
+    private volatile IOException bindException;
 
-    private boolean hasBinded = false;
+    private volatile boolean hasBinded = false;
 
     public ServerRunnable(NanoHTTPD httpd, int timeout) {
         this.httpd = httpd;