Fix NullPointerException in AnimLayer.update()

[capdevon]

java.lang.NullPointerException: Cannot invoke
"com.jme3.anim.tween.action.Action.setMask(com.jme3.anim.AnimationMask)"
because "this.currentAction" is null
        at com.jme3.anim.AnimLayer.update(AnimLayer.java:209)
        at com.jme3.anim.AnimComposer.controlUpdate(AnimComposer.java:391)
        at com.jme3.scene.control.AbstractControl.update(AbstractControl.java:118)
        at com.jme3.scene.Spatial.runControlUpdate(Spatial.java:743)
        at com.jme3.scene.Spatial.updateLogicalState(Spatial.java:890)
        at com.jme3.scene.Node.updateLogicalState(Node.java:228)
        at com.jme3.scene.Node.updateLogicalState(Node.java:239)

Edit:
Link to the forum post: https://hub.jmonkeyengine.org/t/v3-5-0-beta-testing/45209/17

Edit 2:
To facilitate the understanding of the problem I also add the explanation of the fix discussed on the forum and suggested by Ali-RS: "the currentAction should be copied into a local variable inside AnimLayer.update() because it might be changed, removed or replaced with new action in Action.interpolate(time)"

For clarity here is a sample code that can cause the exception:

class NonLoopingAction extends BaseAction {

    ...
     public boolean interpolate(double t) {
        var result = delegate.interpolate(t);
        if (!result) {
            composer.removeCurrentAction(AnimComposer.DEFAULT_LAYER);
        }
        return result;
    }
}

[Ali-RS]

Looks good to me, thank you @capdevon!

Unless there's substantial discussion, I plan to integrate this in about 24 hours.

[stephengold]

Does the choice of variable name count as substantial discussion?

[Ali-RS]

Does the choice of variable name count as substantial discussion?

Yes, I think so.

Please continue the discussion about the variable name, I will delay the merge until we resolve it. Thanks!

[stephengold]

Thanks @capdevon and @Ali-RS !

[stephengold]

Confirmed fixed in v3.5.0-beta6 ... https://hub.jmonkeyengine.org/t/v3-5-0-beta-testing/45209/26