postprocessing target textures: always use nearest filtering

* There's almost never a good reason to use linear filtering for postprocess textures
 * If it is really required, it should be enabled explicitly

jme3-core/src/main/java/com/jme3/texture/Texture2D.java

@@ -60,7 +60,7 @@ public class Texture2D extends Texture {
     public Texture2D(Image img){
         super();
         setImage(img);
-        if (img.getFormat().isDepthFormat()){
+        if (img.getData(0) == null) {
             setMagFilter(MagFilter.Nearest);
             setMinFilter(MinFilter.NearestNoMipMaps);
         }