Fix up Android asset directory scan

AerofoilAndroid/app/src/main/java/org/glideport/game/GpActivity.java

@@ -1,7 +1,30 @@
 package org.glideport.game;
 
 import org.libsdl.app.SDLActivity;
+import android.content.res.AssetManager;
+import android.os.Bundle;
 
 public class GpActivity extends SDLActivity
 {
+    private AssetManager assetManager;
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState)
+    {
+        super.onCreate(savedInstanceState);
+
+        assetManager = getAssets();
+    }
+
+    public String[] scanAssetDirectory(String directory)
+    {
+        try
+        {
+            return this.assetManager.list(directory);
+        }
+        catch (java.io.IOException ex)
+        {
+            return new String[0];
+        }
+    }
 }