fix for issue #1003 (Loading multiple GLB files with animations fails)

jme3-plugins/src/gltf/java/com/jme3/scene/plugins/gltf/GlbLoader.java

@@ -18,6 +18,7 @@ public class GlbLoader extends GltfLoader {
 
     @Override
     public Object load(AssetInfo assetInfo) throws IOException {
+        data.clear();
         LittleEndien stream = new LittleEndien(new DataInputStream(assetInfo.openStream()));
         int magic = stream.readInt();
         int version = stream.readInt();