check if instance is of Savable instead for wider compatibility

clean up a few rows

jme3-core/src/main/java/com/jme3/anim/AnimComposer.java

@@ -66,9 +66,7 @@ public class AnimComposer extends AbstractControl {
      * Instantiate a composer with a single layer, no actions, and no clips.
      */
     public AnimComposer() {
-        if(layers.isEmpty()) {
-            layers.put(DEFAULT_LAYER, new AnimLayer(DEFAULT_LAYER, null));
-        }
+        layers.put(DEFAULT_LAYER, new AnimLayer(DEFAULT_LAYER, null));
     }
 
     /**

jme3-core/src/main/java/com/jme3/anim/AnimLayer.java

@@ -313,8 +313,8 @@ public class AnimLayer implements JmeCloneable, Savable {
     public void write(JmeExporter ex) throws IOException {
         OutputCapsule oc = ex.getCapsule(this);
         oc.write(name, "name", null);
-        if(mask instanceof ArmatureMask) {
-            oc.write((ArmatureMask) mask, "mask", null);
+        if(mask instanceof Savable) {
+            oc.write((Savable) mask, "mask", null);
         }
     }