J3MLoader Fix for default textures for j3md

[riccardobl]

In j3md you should be allowed to define default textures like this

Texture2D Texture -LINEAR: MinTrilinear MagBilinear /path/to/my/texture.dds

But the j3md loaded actually didn't set the default value for texture params.
This pr fixes that.

[stephengold]

Is there a test case or example?

[riccardobl]

TestDefaultTex.java

package tests;

import com.jme3.app.SimpleApplication;
import com.jme3.material.Material;
import com.jme3.renderer.queue.RenderQueue.Bucket;
import com.jme3.scene.Geometry;
import com.jme3.scene.shape.Quad;

public class TestDefaultTex extends SimpleApplication {


    public static void main(String[] args){
        new TestDefaultTex().start();
    }

    @Override
    public void simpleInitApp() {
        Quad quadMesh = new Quad(512,512);
        Geometry quad = new Geometry("Quad", quadMesh);
        quad.setQueueBucket(Bucket.Gui);
        quad.setMaterial(new Material(assetManager, "TestMaterials/TestDefaultTexture.j3md"));  
        guiNode.attachChild(quad);

        quad = quad.clone();
        quad.setMaterial(new Material(assetManager, "TestMaterials/TestMissingTexture.j3md"));
        guiNode.attachChild(quad);
        quad.setLocalTranslation(522,0,0);
    }

    @Override
    public void simpleUpdate(float tpf){
    
    }
}

TestMaterials/TestDefaultTexture.j3md

MaterialDef TestDefaultTexture {

    MaterialParameters {
        Texture2D ColorMap: Flip Textures/ColoredTex/Monkey.png
    }

    Technique {
        VertexShader GLSL100 GLSL150:   Common/MatDefs/Misc/Unshaded.vert
        FragmentShader GLSL100 GLSL150: Common/MatDefs/Misc/Unshaded.frag

        WorldParameters {
            WorldViewProjectionMatrix
            ViewProjectionMatrix
            ViewMatrix
        }

        Defines {
            HAS_COLORMAP : ColorMap
        }
    }
}

TestMaterials/TestMissingTexture.j3md

MaterialDef TestMissingDefaultTexture {

    MaterialParameters {
        Texture2D ColorMap: Texture/that/doesnt/exist.png
    }

    Technique {
        VertexShader GLSL100 GLSL150:   Common/MatDefs/Misc/Unshaded.vert
        FragmentShader GLSL100 GLSL150: Common/MatDefs/Misc/Unshaded.frag

        WorldParameters {
            WorldViewProjectionMatrix
            ViewProjectionMatrix
            ViewMatrix
        }

        Defines {
            HAS_COLORMAP : ColorMap
        }
    }
}

Expected output