* InputManager will throw exception if joysticks are disabled instead of returning null

* Allow use of negative program IDs in LwjglRenderer (will continue instead of crashing for "Invalid ID received from driver" errors)

git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@9116 75d07b2b-3a1a-0410-a2c5-0572b91ccdca

engine/src/core/com/jme3/input/InputManager.java

@@ -651,6 +651,9 @@ public class InputManager implements RawInputListener {
      * @return an array of all joysticks installed on the system.
      */
     public Joystick[] getJoysticks() {
+	   if (joyInput == null){
+            throw new InvalidStateException("Joystick Input is disabled");
+        }
         return joysticks;
     }