WireFrustum lacks a no-arg constructor

[stephengold]

In order for load/save to work, each savable class should have a no-arg constructor.

Sourcecode reference:

jmonkeyengine/jme3-core/src/main/java/com/jme3/scene/debug/WireFrustum.java

Line 44 in a79be13

public WireFrustum(Vector3f[] points){

Forum reference: https://hub.jmonkeyengine.org/t/solved-viewing-frustum/44209/10

[stephengold]

Fixed in "master" branch at 21be3f0